Re: [PATCH v2 -next 1/4] RISC-V: ACPI: Enhance acpi_os_ioremap with MMIO remapping

[Sunil V L]

Hi Alex,

On Tue, Oct 03, 2023 at 08:53:12PM +0200, Alexandre Ghiti wrote:
> Hi Sunil,
> 
> On Wed, Sep 27, 2023 at 7:00 PM Sunil V L <sunilvl@xxxxxxxxxxxxxxxx> wrote:
> >
> > Enhance the acpi_os_ioremap() to support opregions in MMIO space. Also,
> > have strict checks using EFI memory map to allow remapping the RAM similar
> > to arm64.
> >
> > Signed-off-by: Sunil V L <sunilvl@xxxxxxxxxxxxxxxx>
> > Reviewed-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>
> > ---
> >  arch/riscv/Kconfig       |  1 +
> >  arch/riscv/kernel/acpi.c | 87 +++++++++++++++++++++++++++++++++++++++-
> >  2 files changed, 86 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index d607ab0f7c6d..ac039cf8af7a 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -39,6 +39,7 @@ config RISCV
> >         select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
> >         select ARCH_HAS_UBSAN_SANITIZE_ALL
> >         select ARCH_HAS_VDSO_DATA
> > +       select ARCH_KEEP_MEMBLOCK
> 
> Shouldn't we restrict this to ACPI?
> 
Sure, Let me update.

> >         select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
> >         select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
> >         select ARCH_STACKWALK
> > diff --git a/arch/riscv/kernel/acpi.c b/arch/riscv/kernel/acpi.c
> > index 56cb2c986c48..e619edc8b0cc 100644
> > --- a/arch/riscv/kernel/acpi.c
> > +++ b/arch/riscv/kernel/acpi.c
> > @@ -14,9 +14,10 @@
> >   */
> >
> >  #include <linux/acpi.h>
> > +#include <linux/efi.h>
> >  #include <linux/io.h>
> > +#include <linux/memblock.h>
> >  #include <linux/pci.h>
> > -#include <linux/efi.h>
> >
> >  int acpi_noirq = 1;            /* skip ACPI IRQ initialization */
> >  int acpi_disabled = 1;
> > @@ -217,7 +218,89 @@ void __init __acpi_unmap_table(void __iomem *map, unsigned long size)
> >
> >  void __iomem *acpi_os_ioremap(acpi_physical_address phys, acpi_size size)
> >  {
> > -       return (void __iomem *)memremap(phys, size, MEMREMAP_WB);
> > +       efi_memory_desc_t *md, *region = NULL;
> > +       pgprot_t prot;
> > +
> > +       if (WARN_ON_ONCE(!efi_enabled(EFI_MEMMAP)))
> > +               return NULL;
> > +
> > +       for_each_efi_memory_desc(md) {
> > +               u64 end = md->phys_addr + (md->num_pages << EFI_PAGE_SHIFT);
> > +
> > +               if (phys < md->phys_addr || phys >= end)
> > +                       continue;
> > +
> > +               if (phys + size > end) {
> > +                       pr_warn(FW_BUG "requested region covers multiple EFI memory regions\n");
> > +                       return NULL;
> > +               }
> > +               region = md;
> > +               break;
> > +       }
> > +
> > +       /*
> > +        * It is fine for AML to remap regions that are not represented in the
> > +        * EFI memory map at all, as it only describes normal memory, and MMIO
> > +        * regions that require a virtual mapping to make them accessible to
> > +        * the EFI runtime services.
> > +        */
> > +       prot = PAGE_KERNEL_IO;
> > +       if (region) {
> > +               switch (region->type) {
> > +               case EFI_LOADER_CODE:
> > +               case EFI_LOADER_DATA:
> > +               case EFI_BOOT_SERVICES_CODE:
> > +               case EFI_BOOT_SERVICES_DATA:
> > +               case EFI_CONVENTIONAL_MEMORY:
> > +               case EFI_PERSISTENT_MEMORY:
> > +                       if (memblock_is_map_memory(phys) ||
> > +                           !memblock_is_region_memory(phys, size)) {
> > +                               pr_warn(FW_BUG "requested region covers kernel memory\n");
> > +                               return NULL;
> > +                       }
> > +
> > +                       /*
> > +                        * Mapping kernel memory is permitted if the region in
> > +                        * question is covered by a single memblock with the
> > +                        * NOMAP attribute set: this enables the use of ACPI
> > +                        * table overrides passed via initramfs.
> > +                        * This particular use case only requires read access.
> > +                        */
> > +                       fallthrough;
> > +
> > +               case EFI_RUNTIME_SERVICES_CODE:
> > +                       /*
> > +                        * This would be unusual, but not problematic per se,
> > +                        * as long as we take care not to create a writable
> > +                        * mapping for executable code.
> > +                        */
> > +                       prot = PAGE_KERNEL_RO;
> > +                       break;
> > +
> > +               case EFI_ACPI_RECLAIM_MEMORY:
> > +                       /*
> > +                        * ACPI reclaim memory is used to pass firmware tables
> > +                        * and other data that is intended for consumption by
> > +                        * the OS only, which may decide it wants to reclaim
> > +                        * that memory and use it for something else. We never
> > +                        * do that, but we usually add it to the linear map
> > +                        * anyway, in which case we should use the existing
> > +                        * mapping.
> > +                        */
> > +                       if (memblock_is_map_memory(phys))
> > +                               return (void __iomem *)__va(phys);
> > +                       fallthrough;
> > +
> > +               default:
> > +                       if (region->attribute & EFI_MEMORY_WB)
> > +                               prot = PAGE_KERNEL;
> > +                       else if ((region->attribute & EFI_MEMORY_WC) ||
> > +                                (region->attribute & EFI_MEMORY_WT))
> > +                               prot = pgprot_writecombine(PAGE_KERNEL);
> 
> I have to ask: why is write-through mapped to write-combined here?
> 
IIUC, write-through ensures the copy in the cache and memory are always
in sync. So, instead of using WB, non-cacheable WC is used as RISC-V
doesn't really define these attributes. Let me know if this is not
correct.

> > +               }
> > +       }
> > +
> > +       return ioremap_prot(phys, size, pgprot_val(prot));
> >  }
> >
> >  #ifdef CONFIG_PCI
> > --
> > 2.39.2
> >
> 
> Like Andrew said in v1, too bad we can't merge that with arm64 instead
> of duplicating.
> 
I agree. But since acpi_os_ioremap() is supposed to be arch function, I
kept is separate. Also, I need feedback from Ard whether we should make
it common and where to add this common function.

> But otherwise, you can add:
> 
> Reviewed-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>
> 

Thanks!
Sunil