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KVM: x86: Always initialize EFER reserved bits on vendor initialization

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EFER reserved bits are statically initialized, and do not reset if a
vendor module is re-loaded. For example, loading kvm_amd with nested=1
removes EFER.SVME (and potentially EFER.LMSLE) from the reserved bits.
Reloading kvm_amd with nested=0 does not add them back, allowing
userspace to set EFER.SVME with nested=0.

Re-initializing EFER reserved bits before configuring them on vendor
initialization.

Cc: stable@vger.kernel.org
Signed-off-by: Yosry Ahmed <yosry@kernel.org>
Link: https://patch.msgid.link/20260713181020.2735367-4-yosry@kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Yosry Ahmed 2026-07-13 18:10:18 +00:00 committed by Sean Christopherson
parent e62392bf39
commit a4b8acd428
3 changed files with 11 additions and 2 deletions
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10
arch/x86/kvm/msrs.c
View File

@ -19,8 +19,7 @@ bool __read_mostly report_ignored_msrs = true;
module_param(report_ignored_msrs, bool, 0644);
EXPORT_SYMBOL_FOR_KVM_INTERNAL(report_ignored_msrs);
/* Enable syscall by default because its emulated by KVM */
static u64 __read_mostly efer_reserved_bits = ~((u64)EFER_SCE);
static u64 __read_mostly efer_reserved_bits;
#define MAX_IO_MSRS 256
@ -650,6 +649,13 @@ static int set_efer(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
return 0;
}
void kvm_init_efer_bits(void)
{
/* Enable syscall by default because its emulated by KVM */
efer_reserved_bits = ~((u64)EFER_SCE);
}
EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_init_efer_bits);
void kvm_enable_efer_bits(u64 mask)
{
efer_reserved_bits &= ~mask;

1
arch/x86/kvm/msrs.h
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@ -58,6 +58,7 @@ int kvm_get_set_one_reg(struct kvm_vcpu *vcpu, unsigned int ioctl,
int kvm_get_reg_list(struct kvm_vcpu *vcpu,
struct kvm_reg_list __user *user_list);
void kvm_init_efer_bits(void);
void kvm_enable_efer_bits(u64);
bool kvm_valid_efer(struct kvm_vcpu *vcpu, u64 efer);
int kvm_emulate_msr_read(struct kvm_vcpu *vcpu, u32 index, u64 *data);

2
arch/x86/kvm/x86.c
View File

@ -6910,6 +6910,8 @@ EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_setup_xss_caps);
static void kvm_setup_efer_caps(void)
{
kvm_init_efer_bits();
if (kvm_cpu_cap_has(X86_FEATURE_LM))
kvm_enable_efer_bits(EFER_LME | EFER_LMA);