Re: [PATCH v5 04/10] x86, efi: Reserve UEFI 2.8 Specific Purpose Memory for dax

[Dan Williams]

On Fri, Sep 13, 2019 at 9:29 AM Ard Biesheuvel
<ard.biesheuvel@xxxxxxxxxx> wrote:
>
> On Fri, 13 Sep 2019 at 17:22, Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
> >
> > On Fri, Sep 13, 2019 at 6:00 AM Ard Biesheuvel
> > <ard.biesheuvel@xxxxxxxxxx> wrote:
> > >
> > > On Fri, 30 Aug 2019 at 03:06, Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
> > > >
> > > > UEFI 2.8 defines an EFI_MEMORY_SP attribute bit to augment the
> > > > interpretation of the EFI Memory Types as "reserved for a specific
> > > > purpose".
> > > >
> > > > The proposed Linux behavior for specific purpose memory is that it is
> > > > reserved for direct-access (device-dax) by default and not available for
> > > > any kernel usage, not even as an OOM fallback.  Later, through udev
> > > > scripts or another init mechanism, these device-dax claimed ranges can
> > > > be reconfigured and hot-added to the available System-RAM with a unique
> > > > node identifier. This device-dax management scheme implements "soft" in
> > > > the "soft reserved" designation by allowing some or all of the
> > > > reservation to be recovered as typical memory. This policy can be
> > > > disabled at compile-time with CONFIG_EFI_SOFT_RESERVE=n, or runtime with
> > > > efi=nosoftreserve.
> > > >
> > > > This patch introduces 2 new concepts at once given the entanglement
> > > > between early boot enumeration relative to memory that can optionally be
> > > > reserved from the kernel page allocator by default. The new concepts
> > > > are:
> > > >
> > > > - E820_TYPE_SOFT_RESERVED: Upon detecting the EFI_MEMORY_SP
> > > >   attribute on EFI_CONVENTIONAL memory, update the E820 map with this
> > > >   new type. Only perform this classification if the
> > > >   CONFIG_EFI_SOFT_RESERVE=y policy is enabled, otherwise treat it as
> > > >   typical ram.
> > > >
> > > > - IORES_DESC_SOFT_RESERVED: Add a new I/O resource descriptor for
> > > >   a device driver to search iomem resources for application specific
> > > >   memory. Teach the iomem code to identify such ranges as "Soft Reserved".
> > > >
> > > > A follow-on change integrates parsing of the ACPI HMAT to identify the
> > > > node and sub-range boundaries of EFI_MEMORY_SP designated memory. For
> > > > now, just identify and reserve memory of this type.
> > > >
> > > > The translation of EFI_CONVENTIONAL_MEMORY + EFI_MEMORY_SP to "soft
> > > > reserved" is x86/E820-only, but other archs could choose to publish
> > > > IORES_DESC_SOFT_RESERVED resources from their platform-firmware memory
> > > > map handlers. Other EFI-capable platforms would need to go audit their
> > > > local usages of EFI_CONVENTIONAL_MEMORY to consider the soft reserved
> > > > case.
> > > >
> > > > Cc: <x86@xxxxxxxxxx>
> > > > Cc: Borislav Petkov <bp@xxxxxxxxx>
> > > > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > > > Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> > > > Cc: Darren Hart <dvhart@xxxxxxxxxxxxx>
> > > > Cc: Andy Shevchenko <andy@xxxxxxxxxxxxx>
> > > > Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> > > > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > > > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > > > Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> > > > Reported-by: kbuild test robot <lkp@xxxxxxxxx>
> > > > Reviewed-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> > > > Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> > >
> > > Hi Dan,
> > >
> > > I understand that non-x86 may be out of scope for you, but this patch
> > > makes changes to x86 and generic code at the same time without regard
> > > for other architectures.
> >
> > Yes, that did give me pause.
> >
> > > I'd prefer it if we could cover ARM cleanly as well right at the start.
> >
> > Let's do it.
> >
> > >
> > > The first step would be to split out the EFI stub changes (i.e., to
> > > avoid allocating memory from EFI_MEMORY_SP regions) and the EFI core
> > > changes from the other changes. Then, I would like to ask for your
> > > help to get the arm64 part implemented where EFI_MEMORY_SP memory gets
> > > registered/reserved in a way that allows the HMAT code (which should
> > > be arch agnostic) to operate in the same way as it does on x86. Would
> > > it be enough to simply memblock_reserve() it and insert the iomem
> > > resource with the soft_reserved attribute?
> > >
> > > Some more comments below.
> > >
> > > > ---
> > > >  Documentation/admin-guide/kernel-parameters.txt |   19 +++++++--
> > > >  arch/x86/Kconfig                                |   21 +++++++++
> > > >  arch/x86/boot/compressed/eboot.c                |    7 +++
> > > >  arch/x86/boot/compressed/kaslr.c                |    4 ++
> > > >  arch/x86/include/asm/e820/types.h               |    8 ++++
> > > >  arch/x86/include/asm/efi-stub.h                 |   11 +++++
> > > >  arch/x86/kernel/e820.c                          |   12 +++++
> > > >  arch/x86/platform/efi/efi.c                     |   51 +++++++++++++++++++++--
> > > >  drivers/firmware/efi/efi.c                      |    3 +
> > > >  drivers/firmware/efi/libstub/efi-stub-helper.c  |   12 +++++
> > > >  include/linux/efi.h                             |    1
> > > >  include/linux/ioport.h                          |    1
> > > >  12 files changed, 139 insertions(+), 11 deletions(-)
> > > >  create mode 100644 arch/x86/include/asm/efi-stub.h
> > > >
> > > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > > > index 1c67acd1df65..dd28f0726309 100644
> > > > --- a/Documentation/admin-guide/kernel-parameters.txt
> > > > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > > > @@ -1152,7 +1152,8 @@
> > > >                         Format: {"off" | "on" | "skip[mbr]"}
> > > >
> > > >         efi=            [EFI]
> > > > -                       Format: { "old_map", "nochunk", "noruntime", "debug" }
> > > > +                       Format: { "old_map", "nochunk", "noruntime", "debug",
> > > > +                                 "nosoftreserve" }
> > > >                         old_map [X86-64]: switch to the old ioremap-based EFI
> > > >                         runtime services mapping. 32-bit still uses this one by
> > > >                         default.
> > > > @@ -1161,6 +1162,12 @@
> > > >                         firmware implementations.
> > > >                         noruntime : disable EFI runtime services support
> > > >                         debug: enable misc debug output
> > > > +                       nosoftreserve: The EFI_MEMORY_SP (Specific Purpose)
> > > > +                       attribute may cause the kernel to reserve the
> > > > +                       memory range for a memory mapping driver to
> > > > +                       claim. Specify efi=nosoftreserve to disable this
> > > > +                       reservation and treat the memory by its base type
> > > > +                       (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM").
> > > >
> > > >         efi_no_storage_paranoia [EFI; X86]
> > > >                         Using this parameter you can use more than 50% of
> > > > @@ -1173,15 +1180,21 @@
> > > >                         updating original EFI memory map.
> > > >                         Region of memory which aa attribute is added to is
> > > >                         from ss to ss+nn.
> > > > +
> > > >                         If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
> > > >                         is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
> > > >                         attribute is added to range 0x100000000-0x180000000 and
> > > >                         0x10a0000000-0x1120000000.
> > > >
> > > > +                       If efi_fake_mem=8G@9G:0x40000 is specified, the
> > > > +                       EFI_MEMORY_SP(0x40000) attribute is added to
> > > > +                       range 0x240000000-0x43fffffff.
> > > > +
> > > >                         Using this parameter you can do debugging of EFI memmap
> > > > -                       related feature. For example, you can do debugging of
> > > > +                       related features. For example, you can do debugging of
> > > >                         Address Range Mirroring feature even if your box
> > > > -                       doesn't support it.
> > > > +                       doesn't support it, or mark specific memory as
> > > > +                       "soft reserved".
> > > >
> > > >         efivar_ssdt=    [EFI; X86] Name of an EFI variable that contains an SSDT
> > > >                         that is to be dynamically loaded by Linux. If there are
> > > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > > > index 4195f44c6a09..bced13503bb1 100644
> > > > --- a/arch/x86/Kconfig
> > > > +++ b/arch/x86/Kconfig
> > > > @@ -1981,6 +1981,27 @@ config EFI_MIXED
> > > >
> > > >            If unsure, say N.
> > > >
> > > > +config EFI_SOFT_RESERVE
> > > > +       bool "Reserve EFI Specific Purpose Memory"
> > > > +       depends on EFI && ACPI_HMAT
> > > > +       default ACPI_HMAT
> > > > +       ---help---
> > > > +         On systems that have mixed performance classes of memory EFI
> > > > +         may indicate specific purpose memory with an attribute (See
> > > > +         EFI_MEMORY_SP in UEFI 2.8). A memory range tagged with this
> > > > +         attribute may have unique performance characteristics compared
> > > > +         to the system's general purpose "System RAM" pool. On the
> > > > +         expectation that such memory has application specific usage,
> > > > +         and its base EFI memory type is "conventional" answer Y to
> > > > +         arrange for the kernel to reserve it as a "Soft Reserved"
> > > > +         resource, and set aside for direct-access (device-dax) by
> > > > +         default. The memory range can later be optionally assigned to
> > > > +         the page allocator by system administrator policy via the
> > > > +         device-dax kmem facility. Say N to have the kernel treat this
> > > > +         memory as "System RAM" by default.
> > > > +
> > > > +         If unsure, say Y.
> > > > +
> > >
> > > This should be in generic code.
> >
> > Agree.
> >
> > >
> > > >  config SECCOMP
> > > >         def_bool y
> > > >         prompt "Enable seccomp to safely compute untrusted bytecode"
> > > > diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
> > > > index d6662fdef300..f2dc5896d770 100644
> > > > --- a/arch/x86/boot/compressed/eboot.c
> > > > +++ b/arch/x86/boot/compressed/eboot.c
> > > > @@ -10,6 +10,7 @@
> > > >  #include <linux/pci.h>
> > > >
> > > >  #include <asm/efi.h>
> > > > +#include <asm/efi-stub.h>
> > > >  #include <asm/e820/types.h>
> > > >  #include <asm/setup.h>
> > > >  #include <asm/desc.h>
> > > > @@ -553,7 +554,11 @@ setup_e820(struct boot_params *params, struct setup_data *e820ext, u32 e820ext_s
> > > >                 case EFI_BOOT_SERVICES_CODE:
> > > >                 case EFI_BOOT_SERVICES_DATA:
> > > >                 case EFI_CONVENTIONAL_MEMORY:
> > > > -                       e820_type = E820_TYPE_RAM;
> > > > +                       if (!efi_nosoftreserve
> > > > +                                       && (d->attribute & EFI_MEMORY_SP))
> > > > +                               e820_type = E820_TYPE_SOFT_RESERVED;
> > > > +                       else
> > > > +                               e820_type = E820_TYPE_RAM;
> > > >                         break;
> > > >
> > > >                 case EFI_ACPI_MEMORY_NVS:
> > > > diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> > > > index 2e53c056ba20..093e84e28b7a 100644
> > > > --- a/arch/x86/boot/compressed/kaslr.c
> > > > +++ b/arch/x86/boot/compressed/kaslr.c
> > > > @@ -38,6 +38,7 @@
> > > >  #include <linux/efi.h>
> > > >  #include <generated/utsrelease.h>
> > > >  #include <asm/efi.h>
> > > > +#include <asm/efi-stub.h>
> > > >
> > > >  /* Macros used by the included decompressor code below. */
> > > >  #define STATIC
> > > > @@ -760,6 +761,9 @@ process_efi_entries(unsigned long minimum, unsigned long image_size)
> > > >                 if (md->type != EFI_CONVENTIONAL_MEMORY)
> > > >                         continue;
> > > >
> > > > +               if (!efi_nosoftreserve && (md->attribute & EFI_MEMORY_SP))
> > > > +                       continue;
> > > > +
> > > >                 if (efi_mirror_found &&
> > > >                     !(md->attribute & EFI_MEMORY_MORE_RELIABLE))
> > > >                         continue;
> > > > diff --git a/arch/x86/include/asm/e820/types.h b/arch/x86/include/asm/e820/types.h
> > > > index c3aa4b5e49e2..314f75d886d0 100644
> > > > --- a/arch/x86/include/asm/e820/types.h
> > > > +++ b/arch/x86/include/asm/e820/types.h
> > > > @@ -28,6 +28,14 @@ enum e820_type {
> > > >          */
> > > >         E820_TYPE_PRAM          = 12,
> > > >
> > > > +       /*
> > > > +        * Special-purpose memory is indicated to the system via the
> > > > +        * EFI_MEMORY_SP attribute. Define an e820 translation of this
> > > > +        * memory type for the purpose of reserving this range and
> > > > +        * marking it with the IORES_DESC_SOFT_RESERVED designation.
> > > > +        */
> > > > +       E820_TYPE_SOFT_RESERVED = 0xefffffff,
> > > > +
> > > >         /*
> > > >          * Reserved RAM used by the kernel itself if
> > > >          * CONFIG_INTEL_TXT=y is enabled, memory of this type
> > > > diff --git a/arch/x86/include/asm/efi-stub.h b/arch/x86/include/asm/efi-stub.h
> > > > new file mode 100644
> > > > index 000000000000..16ebd036387b
> > > > --- /dev/null
> > > > +++ b/arch/x86/include/asm/efi-stub.h
> > > > @@ -0,0 +1,11 @@
> > > > +// SPDX-License-Identifier: GPL-2.0
> > > > +#ifndef _X86_EFI_STUB_H_
> > > > +#define _X86_EFI_STUB_H_
> > > > +
> > > > +#ifdef CONFIG_EFI_STUB
> > > > +extern bool efi_nosoftreserve;
> > > > +#else
> > > > +#define efi_nosoftreserve (1)
> > > > +#endif
> > > > +
> > > > +#endif /* _X86_EFI_STUB_H_ */
> > >
> > > Please put this in generic code as well (but you need a function not a
> > > variable - see below)
> > >
> > > > diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
> > > > index 7da2bcd2b8eb..9976106b57ec 100644
> > > > --- a/arch/x86/kernel/e820.c
> > > > +++ b/arch/x86/kernel/e820.c
> > > > @@ -190,6 +190,7 @@ static void __init e820_print_type(enum e820_type type)
> > > >         case E820_TYPE_RAM:             /* Fall through: */
> > > >         case E820_TYPE_RESERVED_KERN:   pr_cont("usable");                      break;
> > > >         case E820_TYPE_RESERVED:        pr_cont("reserved");                    break;
> > > > +       case E820_TYPE_SOFT_RESERVED:   pr_cont("soft reserved");               break;
> > > >         case E820_TYPE_ACPI:            pr_cont("ACPI data");                   break;
> > > >         case E820_TYPE_NVS:             pr_cont("ACPI NVS");                    break;
> > > >         case E820_TYPE_UNUSABLE:        pr_cont("unusable");                    break;
> > > > @@ -1037,6 +1038,7 @@ static const char *__init e820_type_to_string(struct e820_entry *entry)
> > > >         case E820_TYPE_PRAM:            return "Persistent Memory (legacy)";
> > > >         case E820_TYPE_PMEM:            return "Persistent Memory";
> > > >         case E820_TYPE_RESERVED:        return "Reserved";
> > > > +       case E820_TYPE_SOFT_RESERVED:   return "Soft Reserved";
> > > >         default:                        return "Unknown E820 type";
> > > >         }
> > > >  }
> > > > @@ -1052,6 +1054,7 @@ static unsigned long __init e820_type_to_iomem_type(struct e820_entry *entry)
> > > >         case E820_TYPE_PRAM:            /* Fall-through: */
> > > >         case E820_TYPE_PMEM:            /* Fall-through: */
> > > >         case E820_TYPE_RESERVED:        /* Fall-through: */
> > > > +       case E820_TYPE_SOFT_RESERVED:   /* Fall-through: */
> > > >         default:                        return IORESOURCE_MEM;
> > > >         }
> > > >  }
> > > > @@ -1064,6 +1067,7 @@ static unsigned long __init e820_type_to_iores_desc(struct e820_entry *entry)
> > > >         case E820_TYPE_PMEM:            return IORES_DESC_PERSISTENT_MEMORY;
> > > >         case E820_TYPE_PRAM:            return IORES_DESC_PERSISTENT_MEMORY_LEGACY;
> > > >         case E820_TYPE_RESERVED:        return IORES_DESC_RESERVED;
> > > > +       case E820_TYPE_SOFT_RESERVED:   return IORES_DESC_SOFT_RESERVED;
> > > >         case E820_TYPE_RESERVED_KERN:   /* Fall-through: */
> > > >         case E820_TYPE_RAM:             /* Fall-through: */
> > > >         case E820_TYPE_UNUSABLE:        /* Fall-through: */
> > > > @@ -1078,11 +1082,12 @@ static bool __init do_mark_busy(enum e820_type type, struct resource *res)
> > > >                 return true;
> > > >
> > > >         /*
> > > > -        * Treat persistent memory like device memory, i.e. reserve it
> > > > -        * for exclusive use of a driver
> > > > +        * Treat persistent memory and other special memory ranges like
> > > > +        * device memory, i.e. reserve it for exclusive use of a driver
> > > >          */
> > > >         switch (type) {
> > > >         case E820_TYPE_RESERVED:
> > > > +       case E820_TYPE_SOFT_RESERVED:
> > > >         case E820_TYPE_PRAM:
> > > >         case E820_TYPE_PMEM:
> > > >                 return false;
> > > > @@ -1285,6 +1290,9 @@ void __init e820__memblock_setup(void)
> > > >                 if (end != (resource_size_t)end)
> > > >                         continue;
> > > >
> > > > +               if (entry->type == E820_TYPE_SOFT_RESERVED)
> > > > +                       memblock_reserve(entry->addr, entry->size);
> > > > +
> > > >                 if (entry->type != E820_TYPE_RAM && entry->type != E820_TYPE_RESERVED_KERN)
> > > >                         continue;
> > > >
> > > > diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
> > > > index 0bb58eb33ca0..9cfb7f1cf25d 100644
> > > > --- a/arch/x86/platform/efi/efi.c
> > > > +++ b/arch/x86/platform/efi/efi.c
> > > > @@ -151,10 +151,18 @@ void __init efi_find_mirror(void)
> > > >   * more than the max 128 entries that can fit in the e820 legacy
> > > >   * (zeropage) memory map.
> > > >   */
> > > > +enum add_efi_mode {
> > > > +       ADD_EFI_ALL,
> > > > +       ADD_EFI_SOFT_RESERVED,
> > > > +};
> > > >
> > > > -static void __init do_add_efi_memmap(void)
> > > > +static void __init do_add_efi_memmap(enum add_efi_mode mode)
> > > >  {
> > > >         efi_memory_desc_t *md;
> > > > +       int add = 0;
> > > > +
> > > > +       if (!efi_enabled(EFI_MEMMAP))
> > > > +               return;
> > > >
> > > >         for_each_efi_memory_desc(md) {
> > > >                 unsigned long long start = md->phys_addr;
> > > > @@ -167,7 +175,10 @@ static void __init do_add_efi_memmap(void)
> > > >                 case EFI_BOOT_SERVICES_CODE:
> > > >                 case EFI_BOOT_SERVICES_DATA:
> > > >                 case EFI_CONVENTIONAL_MEMORY:
> > > > -                       if (md->attribute & EFI_MEMORY_WB)
> > > > +                       if (efi_enabled(EFI_MEM_SOFT_RESERVE)
> > > > +                                       && (md->attribute & EFI_MEMORY_SP))
> > > > +                               e820_type = E820_TYPE_SOFT_RESERVED;
> > > > +                       else if (md->attribute & EFI_MEMORY_WB)
> > > >                                 e820_type = E820_TYPE_RAM;
> > > >                         else
> > > >                                 e820_type = E820_TYPE_RESERVED;
> > > > @@ -193,9 +204,17 @@ static void __init do_add_efi_memmap(void)
> > > >                         e820_type = E820_TYPE_RESERVED;
> > > >                         break;
> > > >                 }
> > > > +
> > > > +               if (e820_type == E820_TYPE_SOFT_RESERVED)
> > > > +                       /* always add E820_TYPE_SOFT_RESERVED */;
> > > > +               else if (mode == ADD_EFI_SOFT_RESERVED)
> > > > +                       continue;
> > > > +
> > > > +               add++;
> > > >                 e820__range_add(start, size, e820_type);
> > > >         }
> > > > -       e820__update_table(e820_table);
> > > > +       if (add)
> > > > +               e820__update_table(e820_table);
> > > >  }
> > > >
> > > >  int __init efi_memblock_x86_reserve_range(void)
> > > > @@ -227,8 +246,18 @@ int __init efi_memblock_x86_reserve_range(void)
> > > >         if (rv)
> > > >                 return rv;
> > > >
> > > > -       if (add_efi_memmap)
> > > > -               do_add_efi_memmap();
> > > > +       if (add_efi_memmap) {
> > > > +               do_add_efi_memmap(ADD_EFI_ALL);
> > > > +       } else {
> > > > +               /*
> > > > +                * Given add_efi_memmap defaults to 0 and there there is no e820
> > > > +                * mechanism for soft-reserved memory. Explicitly scan for
> > > > +                * soft-reserved memory. Otherwise, the mechanism to disable the
> > > > +                * kernel's consideration of EFI_MEMORY_SP is the
> > > > +                * efi=nosoftreserve option.
> > > > +                */
> > > > +               do_add_efi_memmap(ADD_EFI_SOFT_RESERVED);
> > > > +       }
> > > >
> > > >         WARN(efi.memmap.desc_version != 1,
> > > >              "Unexpected EFI_MEMORY_DESCRIPTOR version %ld",
> > > > @@ -781,6 +810,15 @@ static bool should_map_region(efi_memory_desc_t *md)
> > > >         if (IS_ENABLED(CONFIG_X86_32))
> > > >                 return false;
> > > >
> > > > +       /*
> > > > +        * EFI specific purpose memory may be reserved by default
> > > > +        * depending on kernel config and boot options.
> > > > +        */
> > > > +       if (md->type == EFI_CONVENTIONAL_MEMORY
> > > > +                       && efi_enabled(EFI_MEM_SOFT_RESERVE)
> > > > +                       && (md->attribute & EFI_MEMORY_SP))
> > > > +               return false;
> > > > +
> > > >         /*
> > > >          * Map all of RAM so that we can access arguments in the 1:1
> > > >          * mapping when making EFI runtime calls.
> > > > @@ -1072,6 +1110,9 @@ static int __init arch_parse_efi_cmdline(char *str)
> > > >         if (parse_option_str(str, "old_map"))
> > > >                 set_bit(EFI_OLD_MEMMAP, &efi.flags);
> > > >
> > > > +       if (parse_option_str(str, "nosoftreserve"))
> > > > +               clear_bit(EFI_MEM_SOFT_RESERVE, &efi.flags);
> > > > +
> > >
> > > Can we move this to the generic efi= handling code?
> >
> > To parse_efi_cmdline() in drivers/fimrware/efi.c? Sure.
> >
> > >
> > > >         return 0;
> > > >  }
> > > >  early_param("efi", arch_parse_efi_cmdline);
> > > > diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> > > > index 363bb9d00fa5..6d54d5c74347 100644
> > > > --- a/drivers/firmware/efi/efi.c
> > > > +++ b/drivers/firmware/efi/efi.c
> > > > @@ -52,6 +52,9 @@ struct efi __read_mostly efi = {
> > > >         .tpm_log                = EFI_INVALID_TABLE_ADDR,
> > > >         .tpm_final_log          = EFI_INVALID_TABLE_ADDR,
> > > >         .mem_reserve            = EFI_INVALID_TABLE_ADDR,
> > > > +#ifdef CONFIG_EFI_SOFT_RESERVE
> > > > +       .flags                  = 1UL << EFI_MEM_SOFT_RESERVE,
> > > > +#endif
> > > >  };
> > > >  EXPORT_SYMBOL(efi);
> > > >
> > >
> > > I'd prefer it if we could call this EFI_MEM_NO_SOFT_RESERVE instead,
> > > and invert the meaning of the bit.
> >
> > ...but that would mean repeat occurrences of
> > "!efi_enabled(EFI_MEM_NO_SOFT_RESERVE)", doesn't the double negative
> > seem less readable to you?
> >
>
> One the one hand, yes. On the other hand, it is the only flag whose
> default is 'enabled' which is also less than ideal.

Ok, I can get on board with "default 0" being the non exception state
of the flags.

>
> > >
> > > > diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
> > > > index 3caae7f2cf56..35ee98a2c00c 100644
> > > > --- a/drivers/firmware/efi/libstub/efi-stub-helper.c
> > > > +++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
> > > > @@ -28,6 +28,7 @@
> > > >  #define EFI_READ_CHUNK_SIZE    (1024 * 1024)
> > > >
> > > >  static unsigned long __chunk_size = EFI_READ_CHUNK_SIZE;
> > > > +bool efi_nosoftreserve;
> > > >
> > >
> > > This needs a getter function if you want to access it from other
> > > compilation units. This has to do with how the early relocation code
> > > handles data symbol references. Please refer to nokaslr() for an
> > > example.
> >
> > Ah, does that mean that the efi_nosoftreserve global variable
> > instances in different compilation units are effectively static the
> > way I currently have them defined?
>
> No, the problem had to do with relocation of GOT entries on some x86
> builds. Then, things got more complicated when I added the 32-bit ARM
> port, which puts other constraints related to how symbols are placed
> in the binary.
>
> So please duplicate the pattern with the static variable and the
> __pure setter, which has proven to be the most robust way to expose
> variables to other compilation units in the stub.

Will do.