Re: [PATCH v5 1/5] KVM: x86: Virtualize CR4.LAM_SUP

[Chao Gao <chao.gao@intel.com>]

On Mon, Feb 27, 2023 at 04:45:43PM +0800, Robert Hoo wrote:
>LAM feature uses CR4 bit[28] (LAM_SUP) to enable/config LAM masking on
>supervisor mode address. To virtualize that, move CR4.LAM_SUP out of
>unconditional CR4_RESERVED_BITS; its reservation now depends on vCPU has
>LAM feature or not.
>
>Not passing through to guest but intercept it, is to avoid read VMCS field
>every time when KVM fetch its value, with expectation that guest won't
>toggle this bit frequently.
>
>There's no other features/vmx_exec_controls connections, therefore no code
>need to be complemented in kvm/vmx_set_cr4().
>
>Signed-off-by: Robert Hoo <robert.hu@linux.intel.com>
>---
> arch/x86/include/asm/kvm_host.h | 3 ++-
> arch/x86/kvm/x86.h              | 2 ++
> 2 files changed, 4 insertions(+), 1 deletion(-)
>
>diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>index f35f1ff4427b..4684896698f4 100644
>--- a/arch/x86/include/asm/kvm_host.h
>+++ b/arch/x86/include/asm/kvm_host.h
>@@ -125,7 +125,8 @@
> 			  | 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_LAM_SUP))
> 
> #define CR8_RESERVED_BITS (~(unsigned long)X86_CR8_TPR)
> 
>diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
>index 9de72586f406..8ec5cc983062 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_LAM))		\
>+		__reserved_bits |= X86_CR4_LAM_SUP;	\
> 	__reserved_bits;                                \
> })

Add X86_CR4_LAM_SUP to cr4_fixed1 in nested_vmx_cr_fixed1_bits_update()
to indicate CR4.LAM_SUP is allowed to be 0 or 1 in VMX operation.

With this fixed,

Reviewed-by: Chao Gao <chao.gao@intel.com>