Messages in this thread Patch in this message | | | Date | Wed, 30 Nov 2022 23:36:48 +0000 | Subject | [PATCH v4 2/4] x86/virt: Force GIF=1 prior to disabling SVM (for reboot flows) | From | Sean Christopherson <> |
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Set GIF=1 prior to disabling SVM to ensure that INIT is recognized if the kernel is disabling SVM in an emergency, e.g. if the kernel is about to jump into a crash kernel or may reboot without doing a full CPU RESET. If GIF is left cleared, the new kernel (or firmware) will be unabled to awaken APs. Eat faults on STGI (due to EFER.SVME=0) as it's possible that SVM could be disabled via NMI shootdown between reading EFER.SVME and executing STGI.
Link: https://lore.kernel.org/all/cbcb6f35-e5d7-c1c9-4db9-fe5cc4de579a@amd.com Cc: stable@vger.kernel.org Cc: Andrew Cooper <Andrew.Cooper3@citrix.com> Cc: Tom Lendacky <thomas.lendacky@amd.com> Signed-off-by: Sean Christopherson <seanjc@google.com> --- arch/x86/include/asm/virtext.h | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/virtext.h b/arch/x86/include/asm/virtext.h index 8757078d4442..0acb14806a74 100644 --- a/arch/x86/include/asm/virtext.h +++ b/arch/x86/include/asm/virtext.h @@ -126,7 +126,18 @@ static inline void cpu_svm_disable(void) wrmsrl(MSR_VM_HSAVE_PA, 0); rdmsrl(MSR_EFER, efer); - wrmsrl(MSR_EFER, efer & ~EFER_SVME); + if (efer & EFER_SVME) { + /* + * Force GIF=1 prior to disabling SVM, e.g. to ensure INIT and + * NMI aren't blocked. Eat faults on STGI, as it #UDs if SVM + * isn't enabled and SVM can be disabled by an NMI callback. + */ + asm_volatile_goto("1: stgi\n\t" + _ASM_EXTABLE(1b, %l[fault]) + ::: "memory" : fault); +fault: + wrmsrl(MSR_EFER, efer & ~EFER_SVME); + } } /** Makes sure SVM is disabled, if it is supported on the CPU -- 2.38.1.584.g0f3c55d4c2-goog
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