[PATCH v4 5/7] KVM: x86: Virtualize LASS and advertise support to userspace

[Sohil Mehta]

From: Zeng Guang <guang.zeng@xxxxxxxxx>

Virtualize Linear Address Space Separation (LASS) by letting the guest
enable CR4.LASS[bit 27]. Allow the guest to set CR4.LASS only if LASS is
enumerated in the guest's CPUID. Set CR4.LASS in the emulated
IA32_VMX_CR4_FIXED1 MSR so that LASS can be enabled in nested VMX
operation as well.

Keep CR4.LASS KVM-owned instead of making it guest-owned. LASS is
expected to be enabled once per vCPU at boot and rarely toggled at
runtime.

LASS is enumerated by CPUID.(EAX=07H,ECX=1):EAX.LASS[bit 6] and only
works in IA-32e mode. Advertise LASS to userspace on 64-bit kernels and
only when it is supported by the host. Notably, it will not be exposed
to userspace if the deprecated vsyscall=emulate mode is set on the
kernel command line.

Signed-off-by: Zeng Guang <guang.zeng@xxxxxxxxx>
Signed-off-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>
Signed-off-by: Sohil Mehta <sohil.mehta@xxxxxxxxx>
---
v4:
 - Split patch diffs and reworded the commit message
 - Use X86_64_F() instead of F()
---
 arch/x86/kvm/cpuid.c   | 1 +
 arch/x86/kvm/regs.h    | 4 +++-
 arch/x86/kvm/vmx/vmx.c | 1 +
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 9e9cf6538a96..c4dbd00f5e4e 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -1029,6 +1029,7 @@ void kvm_initialize_cpu_caps(void)
 		F(SM4),
 		F(AVX_VNNI),
 		F(AVX512_BF16),
+		X86_64_F(LASS),
 		F(CMPCCXADD),
 		F(FZRM),
 		F(FSRS),
diff --git a/arch/x86/kvm/regs.h b/arch/x86/kvm/regs.h
index 447f0ec3e63e..be8621695c41 100644
--- a/arch/x86/kvm/regs.h
+++ b/arch/x86/kvm/regs.h
@@ -28,7 +28,7 @@ static_assert(!(KVM_POSSIBLE_CR0_GUEST_BITS & X86_CR0_PDPTR_BITS));
 			  | 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_LAM_SUP | X86_CR4_CET))
+			  | X86_CR4_LAM_SUP | X86_CR4_CET | X86_CR4_LASS))
 
 #define CR8_RESERVED_BITS (~(unsigned long)X86_CR8_TPR)
 
@@ -405,6 +405,8 @@ static inline bool __kvm_is_valid_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 		__reserved_bits |= X86_CR4_PCIDE;       \
 	if (!__cpu_has(__c, X86_FEATURE_LAM))           \
 		__reserved_bits |= X86_CR4_LAM_SUP;     \
+	if (!__cpu_has(__c, X86_FEATURE_LASS))          \
+		__reserved_bits |= X86_CR4_LASS;        \
 	if (!__cpu_has(__c, X86_FEATURE_SHSTK) &&       \
 	    !__cpu_has(__c, X86_FEATURE_IBT))           \
 		__reserved_bits |= X86_CR4_CET;         \
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index ecd105f35c78..3082195906da 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7885,6 +7885,7 @@ static void nested_vmx_cr_fixed1_bits_update(struct kvm_vcpu *vcpu)
 
 	entry = kvm_find_cpuid_entry_index(vcpu, 0x7, 1);
 	cr4_fixed1_update(X86_CR4_LAM_SUP,    eax, feature_bit(LAM));
+	cr4_fixed1_update(X86_CR4_LASS,       eax, feature_bit(LASS));
 
 #undef cr4_fixed1_update
 }
-- 
2.43.0