Re: [PATCH 12/13] arm64: Add a capability for FEAT_EVC

On Mon, Aug 9, 2021 at 9:30 AM Oliver Upton [off-list ref] wrote:

Hi Marc,

On Mon, Aug 9, 2021 at 8:48 AM Marc Zyngier [off-list ref] wrote:

quoted

Add a new capability to detect the Enhanced Counter Virtualization
feature (FEAT_EVC).

s/FEAT_EVC/FEAT_ECV/g

quoted

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/kernel/cpufeature.c | 10 ++++++++++
 arch/arm64/tools/cpucaps       |  1 +
 2 files changed, 11 insertions(+)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 0ead8bfedf20..9c2ce5408811 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c

@@ -1899,6 +1899,16 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
                .sign = FTR_UNSIGNED,
                .min_field_value = 1,
        },
+       {
+               .desc = "Enhanced counter virtualization",
+               .capability = ARM64_HAS_ECV,
+               .type = ARM64_CPUCAP_SYSTEM_FEATURE,
+               .matches = has_cpuid_feature,
+               .sys_reg = SYS_ID_AA64MMFR0_EL1,
+               .field_pos = ID_AA64MMFR0_ECV_SHIFT,
+               .sign = FTR_UNSIGNED,
+               .min_field_value = 1,
+       },

Per one of your other patches in the series, it sounds like userspace
access to the self-synchronized registers hasn't been settled yet.
However, if/when available to userspace, should this cpufeature map to
an ELF HWCAP?

Also, w.r.t. my series I have out for ECV in KVM. All the controls
used in EL2 depend on ECV=0x2. I agree that ECV=0x1 needs a cpufeature
bit, but what about EL2's use case?

Forgot to link the series:

http://lore.kernel.org/r/20210804085819.846610-1-oupton@google.com (local)

Besides the typo:

Reviewed-by: Oliver Upton <redacted>

--
Thanks,
Oliver

quoted

 #ifdef CONFIG_ARM64_PAN
        {
                .desc = "Privileged Access Never",

diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
index 49305c2e6dfd..7a7c58acd8f0 100644
--- a/arch/arm64/tools/cpucaps
+++ b/arch/arm64/tools/cpucaps

@@ -18,6 +18,7 @@ HAS_CRC32
 HAS_DCPODP
 HAS_DCPOP
 HAS_E0PD
+HAS_ECV
 HAS_EPAN
 HAS_GENERIC_AUTH
 HAS_GENERIC_AUTH_ARCH
--

2.30.2

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel