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 5.4-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-5.4 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
@@ -120,7 +120,21 @@ 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-5.4/x86-virt-force-gif-1-prior-to-disabling-svm-for-reboot-flows.patch
queue-5.4/x86-reboot-disable-svm-not-just-vmx-when-stopping-cpus.patch
queue-5.4/x86-reboot-disable-virtualization-in-an-emergency-if-svm-is-supported.patch
queue-5.4/x86-crash-disable-virt-in-core-nmi-crash-handler-to-avoid-double-shootdown.patch
queue-5.4/kvm-destroy-target-device-if-coalesced-mmio-unregistration-fails.patch
