| Message ID | 20231010103139.3113421-34-mark.rutland@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: Remove cpus_have_const_cap() | expand |
On Tue, Oct 10, 2023 at 11:31:34AM +0100, Mark Rutland wrote: > static void elf_hwcap_fixup(void) > { > -#ifdef CONFIG_ARM64_ERRATUM_1742098 > - if (cpus_have_const_cap(ARM64_WORKAROUND_1742098)) > + if (cpus_have_cap(ARM64_WORKAROUND_1742098)) > compat_elf_hwcap2 &= ~COMPAT_HWCAP2_AES; > -#endif /* ARM64_ERRATUM_1742098 */ > } The kbuild test robot pointed out that this is broken for CONFIG_COMPAT=n, since compat_elf_hwcap2 is only defined when CONFIG_COMPAT=y. As CONFIG_ARM64_ERRATUM_1742098 depends on CONFIG_COMPAT, this worked prior to this patch. I've changed that locally to: | static void elf_hwcap_fixup(void) | { | #ifdef CONFIG_COMPAT | if (cpus_have_cap(ARM64_WORKAROUND_1742098)) | compat_elf_hwcap2 &= ~COMPAT_HWCAP2_AES; | #endif /* CONFIG_COMPAT */ | } ... since the ifdeffery is protecting the use of 'compat_elf_hwcap2', and the cpucap is now elided by virtue of cpucap_is_possible(). Catalin, aside from the minor fixup above, are you happy to pick this for v6.7? I can post a v4 with that change (and the commit message updated accordingly). Mark.
On Fri, Oct 13, 2023 at 11:53:53AM +0100, Mark Rutland wrote: > On Tue, Oct 10, 2023 at 11:31:34AM +0100, Mark Rutland wrote: > > static void elf_hwcap_fixup(void) > > { > > -#ifdef CONFIG_ARM64_ERRATUM_1742098 > > - if (cpus_have_const_cap(ARM64_WORKAROUND_1742098)) > > + if (cpus_have_cap(ARM64_WORKAROUND_1742098)) > > compat_elf_hwcap2 &= ~COMPAT_HWCAP2_AES; > > -#endif /* ARM64_ERRATUM_1742098 */ > > } > > The kbuild test robot pointed out that this is broken for CONFIG_COMPAT=n, > since compat_elf_hwcap2 is only defined when CONFIG_COMPAT=y. As > CONFIG_ARM64_ERRATUM_1742098 depends on CONFIG_COMPAT, this worked prior to this patch. > > I've changed that locally to: > > | static void elf_hwcap_fixup(void) > | { > | #ifdef CONFIG_COMPAT > | if (cpus_have_cap(ARM64_WORKAROUND_1742098)) > | compat_elf_hwcap2 &= ~COMPAT_HWCAP2_AES; > | #endif /* CONFIG_COMPAT */ > | } > > ... since the ifdeffery is protecting the use of 'compat_elf_hwcap2', and the > cpucap is now elided by virtue of cpucap_is_possible(). > > Catalin, aside from the minor fixup above, are you happy to pick this for v6.7? > > I can post a v4 with that change (and the commit message updated accordingly). I can pick it up and fold the above in. Not sure what you want to update the commit message to (just mention the need for #ifdef CONFIG_COMPAT?)
On Fri, Oct 13, 2023 at 07:04:57PM +0100, Catalin Marinas wrote: > On Fri, Oct 13, 2023 at 11:53:53AM +0100, Mark Rutland wrote: > > On Tue, Oct 10, 2023 at 11:31:34AM +0100, Mark Rutland wrote: > > > static void elf_hwcap_fixup(void) > > > { > > > -#ifdef CONFIG_ARM64_ERRATUM_1742098 > > > - if (cpus_have_const_cap(ARM64_WORKAROUND_1742098)) > > > + if (cpus_have_cap(ARM64_WORKAROUND_1742098)) > > > compat_elf_hwcap2 &= ~COMPAT_HWCAP2_AES; > > > -#endif /* ARM64_ERRATUM_1742098 */ > > > } > > > > The kbuild test robot pointed out that this is broken for CONFIG_COMPAT=n, > > since compat_elf_hwcap2 is only defined when CONFIG_COMPAT=y. As > > CONFIG_ARM64_ERRATUM_1742098 depends on CONFIG_COMPAT, this worked prior to this patch. > > > > I've changed that locally to: > > > > | static void elf_hwcap_fixup(void) > > | { > > | #ifdef CONFIG_COMPAT > > | if (cpus_have_cap(ARM64_WORKAROUND_1742098)) > > | compat_elf_hwcap2 &= ~COMPAT_HWCAP2_AES; > > | #endif /* CONFIG_COMPAT */ > > | } > > > > ... since the ifdeffery is protecting the use of 'compat_elf_hwcap2', and the > > cpucap is now elided by virtue of cpucap_is_possible(). > > > > Catalin, aside from the minor fixup above, are you happy to pick this for v6.7? > > > > I can post a v4 with that change (and the commit message updated accordingly). > > I can pick it up and fold the above in. I've just spotted another ifdeffery issue (leading to cpu_enable_fpsimd() not bdeing defined in some configs), so I'll send a v4 with both issues fixed. > Not sure what you want to update the commit message to (just mention the need > for #ifdef CONFIG_COMPAT?) I was thinknig to replace the last paragraph of the commit message with: | This patch replaces the use of cpus_have_const_cap() with | cpus_have_cap(), which will only generate the bitmap test and avoid | generating an alternative sequence, resulting in slightly simpler annd | smaller code being generated. For consistenct with other cpucaps, the | ARM64_WORKAROUND_1742098 cpucap is added to cpucap_is_possible() so that | code can be elided when this is not possible. However, as we only define | compat_elf_hwcap2 when CONFIG_COMPAT=y, some ifdeffery is still required | within user_feature_fixup() to avoid build errors when CONFIG_COMPAT=n. As above, I'll send a v4 with that folded in. Thanks, Mark.
diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h index 68b0a658e0828..5613d9e813b20 100644 --- a/arch/arm64/include/asm/cpucaps.h +++ b/arch/arm64/include/asm/cpucaps.h @@ -46,6 +46,8 @@ cpucap_is_possible(const unsigned int cap) return IS_ENABLED(CONFIG_UNMAP_KERNEL_AT_EL0); case ARM64_WORKAROUND_843419: return IS_ENABLED(CONFIG_ARM64_ERRATUM_843419); + case ARM64_WORKAROUND_1742098: + return IS_ENABLED(CONFIG_ARM64_ERRATUM_1742098); case ARM64_WORKAROUND_2658417: return IS_ENABLED(CONFIG_ARM64_ERRATUM_2658417); } diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index 9ab7e19b71762..a65c6f00deec5 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -2221,10 +2221,8 @@ static void user_feature_fixup(void) static void elf_hwcap_fixup(void) { -#ifdef CONFIG_ARM64_ERRATUM_1742098 - if (cpus_have_const_cap(ARM64_WORKAROUND_1742098)) + if (cpus_have_cap(ARM64_WORKAROUND_1742098)) compat_elf_hwcap2 &= ~COMPAT_HWCAP2_AES; -#endif /* ARM64_ERRATUM_1742098 */ } #ifdef CONFIG_KVM
In elf_hwcap_fixup() we use cpus_have_const_cap() to check for ARM64_WORKAROUND_1742098, but this is not necessary and cpus_have_cap() would be preferable. For historical reasons, cpus_have_const_cap() is more complicated than it needs to be. Before cpucaps are finalized, it will perform a bitmap test of the system_cpucaps bitmap, and once cpucaps are finalized it will use an alternative branch. This used to be necessary to handle some race conditions in the window between cpucap detection and the subsequent patching of alternatives and static branches, where different branches could be out-of-sync with one another (or w.r.t. alternative sequences). Now that we use alternative branches instead of static branches, these are all patched atomically w.r.t. one another, and there are only a handful of cases that need special care in the window between cpucap detection and alternative patching. Due to the above, it would be nice to remove cpus_have_const_cap(), and migrate callers over to alternative_has_cap_*(), cpus_have_final_cap(), or cpus_have_cap() depending on when their requirements. This will remove redundant instructions and improve code generation, and will make it easier to determine how each callsite will behave before, during, and after alternative patching. The ARM64_WORKAROUND_1742098 cpucap is detected and patched before elf_hwcap_fixup() can run, and hence it is not necessary to use cpus_have_const_cap(). We run cpus_have_const_cap() at most twice: once after finalizing system cpucaps, and potentially once more after detecting mismatched CPUs which support AArch32 at EL0. Due to this, it's not necessary to optimize for many calls to elf_hwcap_fixup(), and it's fine to use cpus_have_cap(). This patch replaces the use of cpus_have_const_cap() with cpus_have_cap(), which will only generate the bitmap test and avoid generating an alternative sequence, resulting in slightly simpler annd smaller code being generated. The ARM64_WORKAROUND_1742098 cpucap is added to cpucap_is_possible() so that code can be elided entirely when this is not possible without requiring ifdeffery or IS_ENABLED() checks at each usage. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: James Morse <james.morse@arm.com> Cc: Suzuki K Poulose <suzuki.poulose@arm.com> Cc: Will Deacon <will@kernel.org> --- arch/arm64/include/asm/cpucaps.h | 2 ++ arch/arm64/kernel/cpufeature.c | 4 +--- 2 files changed, 3 insertions(+), 3 deletions(-)