[PATCH v1 2/6] KVM: x86: Virtualize CR4.LASS

From: Zeng Guang <guang.zeng@intel.com>
To: Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <seanjc@google.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	H Peter Anvin <hpa@zytor.com>,
	kvm@vger.kernel.org
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
	Zeng Guang <guang.zeng@intel.com>
Subject: [PATCH v1 2/6] KVM: x86: Virtualize CR4.LASS
Date: Thu,  1 Jun 2023 22:23:05 +0800	[thread overview]
Message-ID: <20230601142309.6307-3-guang.zeng@intel.com> (raw)
In-Reply-To: <20230601142309.6307-1-guang.zeng@intel.com>

Virtualize CR4.LASS[bit 27] under KVM control instead of being guest-owned
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.

Updating cr4_fixed1 to set CR4.LASS bit in the emulated IA32_VMX_CR4_FIXED1
MSR for guests and allow guests to enable LASS in nested VMX operaion 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@intel.com>
Tested-by: Xuelian Guo <xuelian.guo@intel.com>
---
 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 fb9d1f2d6136..92d8e65fe88c 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 44fb619803b8..a33205ded85c 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7603,6 +7603,9 @@ 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 c544602d07a3..e1295f490308 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -529,6 +529,8 @@ 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;                                \
 })
 
-- 
2.27.0

