[PATCH 6.12 225/567] KVM: nSVM: Propagate SVM_EXIT_CR0_SEL_WRITE correctly for LMSW emulation

Greg Kroah-Hartman
2026-01-06T17:26:37Z

From: Yosry Ahmed <yosry.ahmed@linux.dev>

commit 5674a76db0213f9db1e4d08e847ff649b46889c0 upstream.

When emulating L2 instructions, svm_check_intercept() checks whether a
write to CR0 should trigger a synthesized #VMEXIT with
SVM_EXIT_CR0_SEL_WRITE. For MOV-to-CR0, SVM_EXIT_CR0_SEL_WRITE is only
triggered if any bit other than CR0.MP and CR0.TS is updated. However,
according to the APM (24593—Rev. 3.42—March 2024, Table 15-7):

The LMSW instruction treats the selective CR0-write
intercept as a non-selective intercept (i.e., it intercepts
regardless of the value being written).

Skip checking the changed bits for x86_intercept_lmsw and always inject
SVM_EXIT_CR0_SEL_WRITE.

Fixes: cfec82cb7d31 ("KVM: SVM: Add intercept check for emulated cr accesses")
Cc: stable@vger.kernel.org
Reported-by: Matteo Rizzo <matteorizzo@google.com>
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
Link: https://patch.msgid.link/20251024192918.3191141-3-yosry.ahmed@linux.dev
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kvm/svm/svm.c | 18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)

--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4675,20 +4675,20 @@ static int svm_check_intercept(struct kv
if (info->intercept == x86_intercept_clts)
break;

- cr0 = vcpu->arch.cr0 & ~SVM_CR0_SELECTIVE_MASK;
- val = info->src_val & ~SVM_CR0_SELECTIVE_MASK;
-
+ /* LMSW always triggers INTERCEPT_SELECTIVE_CR0 */
if (info->intercept == x86_intercept_lmsw) {
- cr0 &= 0xfUL;
- val &= 0xfUL;
- /* lmsw can't clear PE - catch this here */
- if (cr0 & X86_CR0_PE)
- val |= X86_CR0_PE;
+ icpt_info.exit_code = SVM_EXIT_CR0_SEL_WRITE;
+ break;
}

+ /*
+ * MOV-to-CR0 only triggers INTERCEPT_SELECTIVE_CR0 if any bit
+ * other than SVM_CR0_SELECTIVE_MASK is changed.
+ */
+ cr0 = vcpu->arch.cr0 & ~SVM_CR0_SELECTIVE_MASK;
+ val = info->src_val & ~SVM_CR0_SELECTIVE_MASK;
if (cr0 ^ val)
icpt_info.exit_code = SVM_EXIT_CR0_SEL_WRITE;
-
break;
}
case SVM_EXIT_READ_DR0: