On Fri, Jan 03, 2025 at 02:26:35PM +0000, Marc Zyngier wrote:
The hwcaps code that exposes SVE features to userspace only considers ID_AA64ZFR0_EL1, while this is only valid when ID_AA64PFR0_EL1.SVE advertises that SVE is actually supported.
The expectations are that when ID_AA64PFR0_EL1.SVE is 0, the ID_AA64ZFR0_EL1 register is also 0. So far, so good.
Things become a bit more interesting if the HW implements SME. In this case, a few ID_AA64ZFR0_EL1 fields indicate *SME* features. And these fields overlap with their SVE interpretations. But the architecture says that the SME and SVE feature sets must match, so we're still hunky-dory.
This goes wrong if the HW implements SME, but not SVE. In this case, we end-up advertising some SVE features to userspace, even if the HW has none. That's because we never consider whether SVE is actually implemented. Oh well.
Fix it by restricting all SVE capabilities to ID_AA64PFR0_EL1.SVE being non-zero.
Reported-by: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Marc Zyngier maz@kernel.org Cc: Will Deacon will@kernel.org Cc: Mark Rutland mark.rutland@arm.com Cc: Mark Brown broonie@kernel.org Cc: stable@vger.kernel.org
I'd add:
Fixes: 06a916feca2b ("arm64: Expose SVE2 features for userspace")
While at the time the code was correct, the architecture messed up our assumptions with the introduction of SME.
@@ -3022,6 +3027,13 @@ static const struct arm64_cpu_capabilities arm64_features[] = { .matches = match, \ } +#define HWCAP_CAP_MATCH_ID(match, reg, field, min_value, cap_type, cap) \
- { \
__HWCAP_CAP(#cap, cap_type, cap) \HWCAP_CPUID_MATCH(reg, field, min_value) \.matches = match, \- }
Do we actually need this macro?
#ifdef CONFIG_ARM64_PTR_AUTH static const struct arm64_cpu_capabilities ptr_auth_hwcap_addr_matches[] = { { @@ -3050,6 +3062,18 @@ static const struct arm64_cpu_capabilities ptr_auth_hwcap_gen_matches[] = { }; #endif +#ifdef CONFIG_ARM64_SVE +static bool has_sve(const struct arm64_cpu_capabilities *cap, int scope) +{
- u64 aa64pfr0 = __read_scoped_sysreg(SYS_ID_AA64PFR0_EL1, scope);
- if (FIELD_GET(ID_AA64PFR0_EL1_SVE, aa64pfr0) < ID_AA64PFR0_EL1_SVE_IMP)
return false;- return has_user_cpuid_feature(cap, scope);
+} +#endif
We can name this has_sve_feature() and use it with the existing HWCAP_CAP_MATCH() macro. I think it would look identical.
We might even be able to use system_supports_sve() directly and avoid changing read_scoped_sysreg(). setup_user_features() is called in smp_cpus_done() after setup_system_features(), so using system_supports_sve() directly should be fine here.