On 8/16/2023 11:46 AM, Huang, Kai wrote:
On Wed, 2023-07-19 at 22:41 +0800, Binbin Wu wrote:
Use the governed feature framework to track if Linear Address Masking (LAM)
is "enabled", i.e. if LAM can be used by the guest. So that guest_can_use()
can be used to support LAM virtualization.
Better to explain why to use governed feature for LAM? Is it because there's
hot path(s) calling guest_cpuid_has()? Anyway some context of why can help
here.
Yes, to avoid calling guest_cpuid_has() in CR3 handling and instruction
emulation paths.
I will add the context next version.
Thanks!
LAM modifies the checking that is applied to 64-bit linear addresses, allowing
software to use of the untranslated address bits for metadata and masks the
metadata bits before using them as linear addresses to access memory.
Signed-off-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>
---
arch/x86/kvm/governed_features.h | 2 ++
arch/x86/kvm/vmx/vmx.c | 3 +++
2 files changed, 5 insertions(+)
diff --git a/arch/x86/kvm/governed_features.h b/arch/x86/kvm/governed_features.h
index 40ce8e6608cd..708578d60e6f 100644
--- a/arch/x86/kvm/governed_features.h
+++ b/arch/x86/kvm/governed_features.h
@@ -5,5 +5,7 @@ BUILD_BUG()
#define KVM_GOVERNED_X86_FEATURE(x) KVM_GOVERNED_FEATURE(X86_FEATURE_##x)
+KVM_GOVERNED_X86_FEATURE(LAM)
+
#undef KVM_GOVERNED_X86_FEATURE
#undef KVM_GOVERNED_FEATURE
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 0ecf4be2c6af..ae47303c88d7 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7783,6 +7783,9 @@ static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
vmx->msr_ia32_feature_control_valid_bits &=
~FEAT_CTL_SGX_LC_ENABLED;
+ if (boot_cpu_has(X86_FEATURE_LAM))
+ kvm_governed_feature_check_and_set(vcpu, X86_FEATURE_LAM);
+
If you want to use boot_cpu_has(), it's better to be done at your last patch to
only set the cap bit when boot_cpu_has() is true, I suppose.
Yes, but new version of kvm_governed_feature_check_and_set() of
KVM-governed feature framework will check against kvm_cpu_cap_has() as well.
I will remove the if statement and call
kvm_governed_feature_check_and_set() directly.
https://lore.kernel.org/kvm/20230815203653.519297-2-seanjc@xxxxxxxxxx/
/* Refresh #PF interception to account for MAXPHYADDR changes. */
vmx_update_exception_bitmap(vcpu);
}
