This is a note to let you know that I've just added the patch titled x86/virt: Force GIF=1 prior to disabling SVM (for reboot flows) to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: x86-virt-force-gif-1-prior-to-disabling-svm-for-reboot-flows.patch and it can be found in the queue-4.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 6a3236580b0b1accc3976345e723104f74f6f8e6 Mon Sep 17 00:00:00 2001 From: Sean Christopherson <seanjc@xxxxxxxxxx> Date: Wed, 30 Nov 2022 23:36:48 +0000 Subject: x86/virt: Force GIF=1 prior to disabling SVM (for reboot flows) From: Sean Christopherson <seanjc@xxxxxxxxxx> 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@xxxxxxx Cc: stable@xxxxxxxxxxxxxxx Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx> Cc: Tom Lendacky <thomas.lendacky@xxxxxxx> Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20221130233650.1404148-3-seanjc@xxxxxxxxxx Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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 @@ -114,7 +114,21 @@ 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 Patches currently in stable-queue which might be from seanjc@xxxxxxxxxx are queue-4.14/x86-virt-force-gif-1-prior-to-disabling-svm-for-reboot-flows.patch queue-4.14/x86-reboot-disable-svm-not-just-vmx-when-stopping-cpus.patch queue-4.14/x86-reboot-disable-virtualization-in-an-emergency-if-svm-is-supported.patch queue-4.14/x86-crash-disable-virt-in-core-nmi-crash-handler-to-avoid-double-shootdown.patch