Re: [PATCH v3 08/17] riscv: Introduce vendor variants of extension helpers

From: Charlie Jenkins
Date: Fri Apr 26 2024 - 16:01:43 EST

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On Fri, Apr 26, 2024 at 05:19:59PM +0100, Conor Dooley wrote:
> On Sat, Apr 20, 2024 at 06:04:40PM -0700, Charlie Jenkins wrote:
> > Vendor extensions are maintained in per-vendor structs (separate from
> > standard extensions which live in riscv_isa). Create vendor variants for
> > the existing extension helpers to interface with the riscv_isa_vendor
> > bitmaps.
>
> > There is a good amount of overlap between these functions, so
> > the alternative checking code can be factored out.
>
> Can you please split this out?

Sure.

>
> >
> > Signed-off-by: Charlie Jenkins <charlie@xxxxxxxxxxxx>
> > ---
> > arch/riscv/errata/sifive/errata.c | 3 ++
> > arch/riscv/errata/thead/errata.c | 3 ++
> > arch/riscv/include/asm/cpufeature.h | 86 +++++++++++++++++-------------
> > arch/riscv/include/asm/vendor_extensions.h | 56 +++++++++++++++++++
> > arch/riscv/kernel/cpufeature.c | 20 ++++---
> > arch/riscv/kernel/vendor_extensions.c | 40 ++++++++++++++
> > 6 files changed, 164 insertions(+), 44 deletions(-)
> >
> > diff --git a/arch/riscv/errata/sifive/errata.c b/arch/riscv/errata/sifive/errata.c
> > index 3d9a32d791f7..b29b6e405ff2 100644
> > --- a/arch/riscv/errata/sifive/errata.c
> > +++ b/arch/riscv/errata/sifive/errata.c
> > @@ -12,6 +12,7 @@
> > #include <asm/alternative.h>
> > #include <asm/vendorid_list.h>
> > #include <asm/errata_list.h>
> > +#include <asm/vendor_extensions.h>
> >
> > struct errata_info_t {
> > char name[32];
> > @@ -99,6 +100,8 @@ void sifive_errata_patch_func(struct alt_entry *begin, struct alt_entry *end,
> > for (alt = begin; alt < end; alt++) {
> > if (alt->vendor_id != SIFIVE_VENDOR_ID)
> > continue;
> > + if (alt->patch_id >= RISCV_VENDOR_EXT_ALTERNATIVES_BASE)
> > + continue;
> > if (alt->patch_id >= ERRATA_SIFIVE_NUMBER) {
> > WARN(1, "This errata id:%d is not in kernel errata list", alt->patch_id);
> > continue;
> > diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c
> > index b1c410bbc1ae..d8e78cc687bc 100644
> > --- a/arch/riscv/errata/thead/errata.c
> > +++ b/arch/riscv/errata/thead/errata.c
> > @@ -18,6 +18,7 @@
> > #include <asm/io.h>
> > #include <asm/patch.h>
> > #include <asm/vendorid_list.h>
> > +#include <asm/vendor_extensions.h>
> >
> > static bool errata_probe_pbmt(unsigned int stage,
> > unsigned long arch_id, unsigned long impid)
> > @@ -163,6 +164,8 @@ void thead_errata_patch_func(struct alt_entry *begin, struct alt_entry *end,
> > for (alt = begin; alt < end; alt++) {
> > if (alt->vendor_id != THEAD_VENDOR_ID)
> > continue;
> > + if (alt->patch_id >= RISCV_VENDOR_EXT_ALTERNATIVES_BASE)
> > + continue;
>
> > if (alt->patch_id >= ERRATA_THEAD_NUMBER)
>
> This number is 2, how does the patching actually work for vendor stuff
> when the base is always greater than 2?
>

Patching is handled through the patcher at the end of cpufeature.c. The
vendor_id field is set in the alternatives for errata and now also for
vendor extensions. The vendor extension patching is all handled
generically.

This is distinguished by the patch_id being greater than
RISCV_VENDOR_EXT_ALTERNATIVES_BASE, which should leave way more than
enough room for errata ids. Since the code already checks if the
patch_id is greater than the errata number, I can drop the
"if (alt->patch_id >= RISCV_VENDOR_EXT_ALTERNATIVES_BASE)" check.

> > continue;
> >
> > diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
> > index db6a6d7d6b2e..83e1143db9ad 100644
> > --- a/arch/riscv/include/asm/cpufeature.h
> > +++ b/arch/riscv/include/asm/cpufeature.h
> > @@ -103,22 +103,13 @@ bool __riscv_isa_extension_available(const unsigned long *isa_bitmap, unsigned i
> > __riscv_isa_extension_available(isa_bitmap, RISCV_ISA_EXT_##ext)
> >
> > static __always_inline bool
> > -riscv_has_extension_likely(const unsigned long ext)
> > +__riscv_has_extension_likely_alternatives(const unsigned long vendor, const unsigned long ext)
> > {
> > - compiletime_assert(ext < RISCV_ISA_EXT_MAX,
> > - "ext must be < RISCV_ISA_EXT_MAX");
> > -
> > - if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
> > - asm goto(
> > - ALTERNATIVE("j %l[l_no]", "nop", 0, %[ext], 1)
> > - :
> > - : [ext] "i" (ext)
> > - :
> > - : l_no);
> > - } else {
> > - if (!__riscv_isa_extension_available(NULL, ext))
> > - goto l_no;
> > - }
> > + asm goto(ALTERNATIVE("j %l[l_no]", "nop", %[vendor], %[ext], 1)
> > + :
> > + : [vendor] "i" (vendor), [ext] "i" (ext)
> > + :
> > + : l_no);
> >
> > return true;
> > l_no:
> > @@ -126,42 +117,65 @@ riscv_has_extension_likely(const unsigned long ext)
> > }
> >
> > static __always_inline bool
> > -riscv_has_extension_unlikely(const unsigned long ext)
> > +__riscv_has_extension_unlikely_alternatives(const unsigned long vendor, const unsigned long ext)
>
> ngl, I think you could drop the _alternatives from these - the
> likely/unlikely is only actually a thing because of the alternatives in
> the first place & just retain the __ as a differentiator. That'd help
> you with some of the long-line wrangling you've been doing below.
>

Sounds good.

> > {
> > - compiletime_assert(ext < RISCV_ISA_EXT_MAX,
> > - "ext must be < RISCV_ISA_EXT_MAX");
> > -
> > - if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
> > - asm goto(
> > - ALTERNATIVE("nop", "j %l[l_yes]", 0, %[ext], 1)
> > - :
> > - : [ext] "i" (ext)
> > - :
> > - : l_yes);
> > - } else {
> > - if (__riscv_isa_extension_available(NULL, ext))
> > - goto l_yes;
> > - }
> > + asm goto(ALTERNATIVE("nop", "j %l[l_yes]", %[vendor], %[ext], 1)
> > + :
> > + : [vendor] "i" (vendor), [ext] "i" (ext)
> > + :
> > + : l_yes);
> >
> > return false;
> > l_yes:
> > return true;
> > }
> >
> > +static __always_inline bool
> > +riscv_has_extension_likely(const unsigned long ext)
>
> Can you format this so that its on one line & wrap the arguments if
> needs be?
>
> > +{
> > + compiletime_assert(ext < RISCV_ISA_EXT_MAX,
> > + "ext must be < RISCV_ISA_EXT_MAX");
> > +
> > + if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE))
> > + return __riscv_has_extension_likely_alternatives(0, ext);
> > + else
>
> I'm almost certain I said this before, but none of the else branches are
> needed here, there's a return in the if branch, so the remainder of the
> function becomes unconditionally executed.

Will fix.

>
> > + return __riscv_isa_extension_available(NULL, ext);
> > +}
> > +
> > +static __always_inline bool
> > +riscv_has_extension_unlikely(const unsigned long ext)
> > +{
> > + compiletime_assert(ext < RISCV_ISA_EXT_MAX,
> > + "ext must be < RISCV_ISA_EXT_MAX");
> > +
> > + if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE))
> > + return __riscv_has_extension_unlikely_alternatives(0, ext);
> > + else
> > + return __riscv_isa_extension_available(NULL, ext);
> > +}
> > +
> > static __always_inline bool riscv_cpu_has_extension_likely(int cpu, const unsigned long ext)
> > {
> > - if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE) && riscv_has_extension_likely(ext))
> > - return true;
> > + compiletime_assert(ext < RISCV_ISA_EXT_MAX,
> > + "ext must be < RISCV_ISA_EXT_MAX");
> >
> > - return __riscv_isa_extension_available(hart_isa[cpu].isa, ext);
> > + if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE) &&
> > + __riscv_has_extension_likely_alternatives(0, ext))
>
> 0 is meaningless, please make this more understandable using a define of
> some sort.

I'll add a define.

>
> > + return true;
> > + else
> > + return __riscv_isa_extension_available(hart_isa[cpu].isa, ext);
> > }
> >
> > static __always_inline bool riscv_cpu_has_extension_unlikely(int cpu, const unsigned long ext)
> > {
> > - if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE) && riscv_has_extension_unlikely(ext))
> > - return true;
> > + compiletime_assert(ext < RISCV_ISA_EXT_MAX,
> > + "ext must be < RISCV_ISA_EXT_MAX");
> >
> > - return __riscv_isa_extension_available(hart_isa[cpu].isa, ext);
> > + if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE) &&
> > + __riscv_has_extension_unlikely_alternatives(0, ext))
> > + return true;
> > + else
> > + return __riscv_isa_extension_available(hart_isa[cpu].isa, ext);
> > }
> >
> > #endif
> > diff --git a/arch/riscv/include/asm/vendor_extensions.h b/arch/riscv/include/asm/vendor_extensions.h
> > index 0af1ddd0af70..3e676a96016e 100644
> > --- a/arch/riscv/include/asm/vendor_extensions.h
> > +++ b/arch/riscv/include/asm/vendor_extensions.h
> > @@ -23,4 +23,60 @@ extern const struct riscv_isa_vendor_ext_data_list *riscv_isa_vendor_ext_list[];
> >
> > extern const size_t riscv_isa_vendor_ext_list_size;
> >
> > +/*
> > + * The alternatives need some way of distinguishing between vendor extensions
> > + * and errata. Incrementing all of the vendor extension keys so they are at
> > + * least 0x8000 accomplishes that.
> > + */
> > +#define RISCV_VENDOR_EXT_ALTERNATIVES_BASE 0x8000
> > +
> > +bool __riscv_isa_vendor_extension_available(int cpu, unsigned long vendor, unsigned int bit);
> > +#define riscv_cpu_isa_vendor_extension_available(cpu, vendor, ext) \
> > + __riscv_isa_vendor_extension_available(cpu, vendor, RISCV_ISA_VENDOR_EXT_##ext)
> > +#define riscv_isa_vendor_extension_available(vendor, ext) \
> > + __riscv_isa_vendor_extension_available(-1, vendor, RISCV_ISA_VENDOR_EXT_##ext)
> > +
> > +static __always_inline bool
> > +riscv_has_vendor_extension_likely(const unsigned long vendor, const unsigned long ext)
> > +{
> > + if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE))
> > + return __riscv_has_extension_likely_alternatives(vendor,
> > + ext + RISCV_VENDOR_EXT_ALTERNATIVES_BASE);
> > + else
> > + return __riscv_isa_vendor_extension_available(-1, vendor, ext);
> > +}
> > +
> > +static __always_inline bool
> > +riscv_has_vendor_extension_unlikely(const unsigned long vendor, const unsigned long ext)
> > +{
> > + if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE))
> > + return __riscv_has_extension_unlikely_alternatives(vendor,
> > + ext + RISCV_VENDOR_EXT_ALTERNATIVES_BASE);
> > + else
> > + return __riscv_isa_vendor_extension_available(-1, vendor, ext);
> > +}
> > +
> > +static __always_inline bool riscv_cpu_has_vendor_extension_likely(const unsigned long vendor,
> > + int cpu, const unsigned long ext)
> > +{
> > + if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE) &&
> > + __riscv_has_extension_likely_alternatives(vendor,
> > + ext + RISCV_VENDOR_EXT_ALTERNATIVES_BASE))
> > + return true;
> > + else
> > + return __riscv_isa_vendor_extension_available(cpu, vendor, ext);
> > +}
> > +
> > +static __always_inline bool riscv_cpu_has_vendor_extension_unlikely(const unsigned long vendor,
> > + int cpu,
> > + const unsigned long ext)
> > +{
> > + if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE) &&
> > + __riscv_has_extension_unlikely_alternatives(vendor,
> > + ext + RISCV_VENDOR_EXT_ALTERNATIVES_BASE))
> > + return true;
> > + else
> > + return __riscv_isa_vendor_extension_available(cpu, vendor, ext);
> > +}
> > +
> > #endif /* _ASM_VENDOR_EXTENSIONS_H */
> > diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> > index c9f36822e337..17371887abcc 100644
> > --- a/arch/riscv/kernel/cpufeature.c
> > +++ b/arch/riscv/kernel/cpufeature.c
> > @@ -833,25 +833,29 @@ void __init_or_module riscv_cpufeature_patch_func(struct alt_entry *begin,
> > {
> > struct alt_entry *alt;
> > void *oldptr, *altptr;
> > - u16 id, value;
> > + u16 id, value, vendor;
> >
> > if (stage == RISCV_ALTERNATIVES_EARLY_BOOT)
> > return;
> >
> > for (alt = begin; alt < end; alt++) {
> > - if (alt->vendor_id != 0)
> > - continue;
> > -
> > id = PATCH_ID_CPUFEATURE_ID(alt->patch_id);
> > + vendor = PATCH_ID_CPUFEATURE_ID(alt->vendor_id);
> >
> > - if (id >= RISCV_ISA_EXT_MAX) {
> > + if (id < RISCV_ISA_EXT_MAX) {
>
> I think any reliance on the standard ext max requires a comment
> explaining what the interaction is between it and the vendor stuff.
>

I'll add a comment describing that anything with an id below
RISCV_ISA_EXT_MAX is interpreted as a standard extension and anything
with an id above RISCV_VENDOR_EXT_ALTERNATIVES_BASE will be interpreted
as a vendor extension.

> > + if (alt->vendor_id != 0)
> > + continue;
>
> If this happens, it's a bug, should we be continuing silently?
>

This indicates that the patch should be treated as errata and that's why
it silently continues. I can add a comment that says that.

- Charlie

> Cheers,
> Conor.
>
> > +
> > + if (!__riscv_isa_extension_available(NULL, id))
> > + continue;
> > + } else if (id >= RISCV_VENDOR_EXT_ALTERNATIVES_BASE) {
> > + if (!__riscv_isa_vendor_extension_available(-1, vendor, id))
> > + continue;
> > + } else {
> > WARN(1, "This extension id:%d is not in ISA extension list", id);
> > continue;
> > }
> >
> > - if (!__riscv_isa_extension_available(NULL, id))
> > - continue;
> > -
> > value = PATCH_ID_CPUFEATURE_VALUE(alt->patch_id);
> > if (!riscv_cpufeature_patch_check(id, value))
> > continue;
> > diff --git a/arch/riscv/kernel/vendor_extensions.c b/arch/riscv/kernel/vendor_extensions.c
> > index f76cb3013c2d..eced93eec5a6 100644
> > --- a/arch/riscv/kernel/vendor_extensions.c
> > +++ b/arch/riscv/kernel/vendor_extensions.c
> > @@ -3,6 +3,7 @@
> > * Copyright 2024 Rivos, Inc
> > */
> >
> > +#include <asm/vendorid_list.h>
> > #include <asm/vendor_extensions.h>
> > #include <asm/vendor_extensions/thead.h>
> >
> > @@ -16,3 +17,42 @@ const struct riscv_isa_vendor_ext_data_list *riscv_isa_vendor_ext_list[] = {
> > };
> >
> > const size_t riscv_isa_vendor_ext_list_size = ARRAY_SIZE(riscv_isa_vendor_ext_list);
> > +
> > +/**
> > + * __riscv_isa_vendor_extension_available() - Check whether given vendor
> > + * extension is available or not.
> > + *
> > + * @cpu: check if extension is available on this cpu
> > + * @vendor: vendor that the extension is a member of
> > + * @bit: bit position of the desired extension
> > + * Return: true or false
> > + *
> > + * NOTE: When cpu is -1, will check if extension is available on all cpus
> > + */
> > +bool __riscv_isa_vendor_extension_available(int cpu, unsigned long vendor, unsigned int bit)
> > +{
> > + unsigned long *bmap;
> > + struct riscv_isainfo *cpu_bmap;
> > + size_t bmap_size;
> > +
> > + switch (vendor) {
> > +#ifdef CONFIG_RISCV_ISA_VENDOR_EXT_THEAD
> > + case THEAD_VENDOR_ID:
> > + bmap = riscv_isa_vendor_ext_list_thead.vendor_bitmap;
> > + cpu_bmap = riscv_isa_vendor_ext_list_thead.per_hart_vendor_bitmap;
> > + bmap_size = riscv_isa_vendor_ext_list_thead.bitmap_size;
> > + break;
> > +#endif
> > + default:
> > + return false;
> > + }
> > +
> > + if (cpu != -1)
> > + bmap = cpu_bmap[cpu].isa;
> > +
> > + if (bit >= bmap_size)
> > + return false;
> > +
> > + return test_bit(bit, bmap) ? true : false;
> > +}
> > +EXPORT_SYMBOL_GPL(__riscv_isa_vendor_extension_available);
> >
> > --
> > 2.44.0
> >

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