[PATCH v10 16/28] KVM: x86: Mark CR4.FRED as not reserved

[Sohil Mehta]

From: "Xin Li (Intel)" <xin@xxxxxxxxx>

The CR4.FRED bit, i.e., CR4[32], is no longer a reserved bit when
guest cpu cap has FRED, i.e.,
  1) All of FRED KVM support is in place.
  2) Guest enumerates FRED.

Otherwise it is still a reserved bit.

Signed-off-by: Xin Li (Intel) <xin@xxxxxxxxx>
Signed-off-by: Sohil Mehta <sohil.mehta@xxxxxxxxx>
---
v10:
 - Check CR4.FRED against IA-32e mode in kvm_set_cr4() instead of
   __kvm_is_valid_cr4(), so that KVM_SET_SREGS no longer rejects a CR4
   and EFER pair that are loaded together (e.g., when restoring a FRED
   guest)
---
 arch/x86/kvm/regs.c | 7 +++++++
 arch/x86/kvm/regs.h | 4 +++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/regs.c b/arch/x86/kvm/regs.c
index 8f66438989e4..ba6c8856b4ff 100644
--- a/arch/x86/kvm/regs.c
+++ b/arch/x86/kvm/regs.c
@@ -429,6 +429,13 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 			return 1;
 	}
 
+	/*
+	 * FRED can not be enabled when EFER.LMA=0.  Note, MOV to CR4 outside
+	 * 64-bit mode clears CR4[63:32] so only emulation can get here.
+	 */
+	if ((cr4 & X86_CR4_FRED) && !is_long_mode(vcpu))
+		return 1;
+
 	if ((cr4 & X86_CR4_CET) && !kvm_is_cr0_bit_set(vcpu, X86_CR0_WP))
 		return 1;
 
diff --git a/arch/x86/kvm/regs.h b/arch/x86/kvm/regs.h
index ef46918daf43..5db01693ad07 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_FRED))
 
 #define CR8_RESERVED_BITS (~(unsigned long)X86_CR8_TPR)
 
@@ -423,6 +423,8 @@ static inline bool __kvm_is_valid_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 	if (!__cpu_has(__c, X86_FEATURE_SHSTK) &&       \
 	    !__cpu_has(__c, X86_FEATURE_IBT))           \
 		__reserved_bits |= X86_CR4_CET;         \
+	if (!__cpu_has(__c, X86_FEATURE_FRED))          \
+		__reserved_bits |= X86_CR4_FRED;        \
 	__reserved_bits;                                \
 })
 
-- 
2.43.0