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x86/virt: Force GIF=1 prior to disabling SVM (for reboot flows)

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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>
This commit is contained in:
Sean Christopherson 2022-11-30 23:36:48 +00:00 committed by Greg Kroah-Hartman
parent 4c9812d989
commit ee80fb1dca
1 changed files with 15 additions and 1 deletions
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16
arch/x86/include/asm/virtext.h
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@ -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