linux-kernel - [PATCH v3 17/27] KVM: x86: Mark CR4.FRED as not reserved when guest can use FRED

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Message-ID: <20241001050110.3643764-18-xin@zytor.com>
Date: Mon, 30 Sep 2024 22:01:00 -0700
From: "Xin Li (Intel)" <xin@...or.com>
To: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org
Cc: seanjc@...gle.com, pbonzini@...hat.com, corbet@....net, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com, luto@...nel.org, peterz@...radead.org,
        andrew.cooper3@...rix.com, xin@...or.com
Subject: [PATCH v3 17/27] KVM: x86: Mark CR4.FRED as not reserved when guest can use FRED

From: Xin Li <xin3.li@...el.com>

The CR4.FRED bit, i.e., CR4[32], is no longer a reserved bit when
guest can use 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 <xin3.li@...el.com>
Signed-off-by: Xin Li (Intel) <xin@...or.com>
Tested-by: Shan Kang <shan.kang@...el.com>
---

Changes since v2:
* Don't allow CR4.FRED=1 before all of FRED KVM support is in place
  (Sean Christopherson).
---
 arch/x86/include/asm/kvm_host.h | 2 +-
 arch/x86/kvm/vmx/vmx.c          | 4 ++++
 arch/x86/kvm/x86.h              | 2 ++
 3 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 3830084b569b..87f9f0b6cf3c 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -136,7 +136,7 @@
 			  | 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_LAM_SUP | X86_CR4_FRED))
 
 #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 03f42b218554..bfdd10773136 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -8009,6 +8009,10 @@ void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 	kvm_governed_feature_check_and_set(vcpu, X86_FEATURE_LAM);
 	kvm_governed_feature_check_and_set(vcpu, X86_FEATURE_FRED);
 
+	/* Don't allow CR4.FRED=1 before all of FRED KVM support is in place. */
+	if (!guest_can_use(vcpu, X86_FEATURE_FRED))
+		vcpu->arch.cr4_guest_rsvd_bits |= X86_CR4_FRED;
+
 	vmx_setup_uret_msrs(vmx);
 
 	if (cpu_has_secondary_exec_ctrls())
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 992e73ee2ec5..0ed91512b757 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -561,6 +561,8 @@ enum kvm_msr_access {
 		__reserved_bits |= X86_CR4_PCIDE;       \
 	if (!__cpu_has(__c, X86_FEATURE_LAM))           \
 		__reserved_bits |= X86_CR4_LAM_SUP;     \
+	if (!__cpu_has(__c, X86_FEATURE_FRED))          \
+		__reserved_bits |= X86_CR4_FRED;        \
 	__reserved_bits;                                \
 })
 
-- 
2.46.2