From: Sean Christopherson seanjc@google.com
commit 6a3236580b0b1accc3976345e723104f74f6f8e6 upstream.
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 Reviewed-by: Thomas Gleixner tglx@linutronix.de Link: https://lore.kernel.org/r/20221130233650.1404148-3-seanjc@google.com Signed-off-by: Sean Christopherson seanjc@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/include/asm/virtext.h | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-)
--- a/arch/x86/include/asm/virtext.h +++ b/arch/x86/include/asm/virtext.h @@ -126,7 +126,21 @@ 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 to ensure INIT and NMI + * aren't blocked, e.g. if a fatal error occurred between CLGI + * and STGI. Note, STGI may #UD if SVM is disabled from NMI + * context between reading EFER and executing STGI. In that + * case, GIF must already be set, otherwise the NMI would have + * been blocked, so just eat the fault. + */ + 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