Re: [PATCH 1/6] KVM: x86: Virtualize CR4.LASS

Zeng Guang <guang.zeng@xxxxxxxxx> · Tue, 25 Apr 2023 09:52:43 +0800

On 4/24/2023 2:45 PM, Binbin Wu wrote:
Reviewed-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>

one nit below

On 4/20/2023 9:37 PM, Zeng Guang wrote:
Virtualize CR4.LASS[bit 27] under KVM control instead of being guest-owned
under control of KVM or under KVM's control

Or just simply use "intercept"?

OK. Will change it.

as CR4.LASS generally set once for each vCPU at boot time and won't be
toggled at runtime. Besides, only if VM has LASS capability enumerated with
CPUID.(EAX=07H.ECX=1):EAX.LASS[bit 6], KVM allows guest software to be able
to set CR4.LASS. By design CR4.LASS can be manipulated by nested guest as
well.

Notes: Setting CR4.LASS to 1 enable LASS in IA-32e mode. It doesn't take
effect in legacy mode even if CR4.LASS is set.

Signed-off-by: Zeng Guang <guang.zeng@xxxxxxxxx>
---
   arch/x86/include/asm/kvm_host.h | 2 +-
   arch/x86/kvm/vmx/vmx.c          | 3 +++
   arch/x86/kvm/x86.h              | 2 ++
   3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 6aaae18f1854..8ff89a52ef66 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -125,7 +125,7 @@
   			  | X86_CR4_PGE | X86_CR4_PCE | X86_CR4_OSFXSR | X86_CR4_PCIDE \
   			  | X86_CR4_OSXSAVE | X86_CR4_SMEP | X86_CR4_FSGSBASE \
   			  | X86_CR4_OSXMMEXCPT | X86_CR4_LA57 | X86_CR4_VMXE \
-			  | X86_CR4_SMAP | X86_CR4_PKE | X86_CR4_UMIP))
+			  | X86_CR4_SMAP | X86_CR4_PKE | X86_CR4_UMIP | X86_CR4_LASS))
   
   #define CR8_RESERVED_BITS (~(unsigned long)X86_CR8_TPR)
   
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 43ff3276918b..c923d7599d71 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7569,6 +7569,9 @@ static void nested_vmx_cr_fixed1_bits_update(struct kvm_vcpu *vcpu)
   	cr4_fixed1_update(X86_CR4_UMIP,       ecx, feature_bit(UMIP));
   	cr4_fixed1_update(X86_CR4_LA57,       ecx, feature_bit(LA57));
   
+	entry = kvm_find_cpuid_entry_index(vcpu, 0x7, 1);
+	cr4_fixed1_update(X86_CR4_LASS,       eax, feature_bit(LASS));
+
   #undef cr4_fixed1_update
   }
   
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 7c8a30d44c29..218f4c73789a 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -475,6 +475,8 @@ bool kvm_msr_allowed(struct kvm_vcpu *vcpu, u32 index, u32 type);
   		__reserved_bits |= X86_CR4_VMXE;        \
   	if (!__cpu_has(__c, X86_FEATURE_PCID))          \
   		__reserved_bits |= X86_CR4_PCIDE;       \
+	if (!__cpu_has(__c, X86_FEATURE_LASS))          \
+		__reserved_bits |= X86_CR4_LASS;        \
   	__reserved_bits;                                \
   })
   






