This is a note to let you know that I've just added the patch titled x86/virt: Eat faults on VMXOFF in 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-eat-faults-on-vmxoff-in-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 aec511ad153556640fb1de38bfe00c69464f997f Mon Sep 17 00:00:00 2001 From: Sean Christopherson <seanjc@xxxxxxxxxx> Date: Wed, 30 Dec 2020 16:26:54 -0800 Subject: x86/virt: Eat faults on VMXOFF in reboot flows From: Sean Christopherson <seanjc@xxxxxxxxxx> commit aec511ad153556640fb1de38bfe00c69464f997f upstream. Silently ignore all faults on VMXOFF in the reboot flows as such faults are all but guaranteed to be due to the CPU not being in VMX root. Because (a) VMXOFF may be executed in NMI context, e.g. after VMXOFF but before CR4.VMXE is cleared, (b) there's no way to query the CPU's VMX state without faulting, and (c) the whole point is to get out of VMX root, eating faults is the simplest way to achieve the desired behaior. Technically, VMXOFF can fault (or fail) for other reasons, but all other fault and failure scenarios are mode related, i.e. the kernel would have to magically end up in RM, V86, compat mode, at CPL>0, or running with the SMI Transfer Monitor active. The kernel is beyond hosed if any of those scenarios are encountered; trying to do something fancy in the error path to handle them cleanly is pointless. Fixes: 1e9931146c74 ("x86: asm/virtext.h: add cpu_vmxoff() inline function") Reported-by: David P. Reed <dpreed@xxxxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> Message-Id: <20201231002702.2223707-2-seanjc@xxxxxxxxxx> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/include/asm/virtext.h | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) --- a/arch/x86/include/asm/virtext.h +++ b/arch/x86/include/asm/virtext.h @@ -30,15 +30,22 @@ static inline int cpu_has_vmx(void) } -/** Disable VMX on the current CPU +/** + * cpu_vmxoff() - Disable VMX on the current CPU * - * vmxoff causes a undefined-opcode exception if vmxon was not run - * on the CPU previously. Only call this function if you know VMX - * is enabled. + * Disable VMX and clear CR4.VMXE (even if VMXOFF faults) + * + * Note, VMXOFF causes a #UD if the CPU is !post-VMXON, but it's impossible to + * atomically track post-VMXON state, e.g. this may be called in NMI context. + * Eat all faults as all other faults on VMXOFF faults are mode related, i.e. + * faults are guaranteed to be due to the !post-VMXON check unless the CPU is + * magically in RM, VM86, compat mode, or at CPL>0. */ static inline void cpu_vmxoff(void) { - asm volatile ("vmxoff"); + asm_volatile_goto("1: vmxoff\n\t" + _ASM_EXTABLE(1b, %l[fault]) :::: fault); +fault: cr4_clear_bits(X86_CR4_VMXE); } Patches currently in stable-queue which might be from seanjc@xxxxxxxxxx are queue-5.4/x86-virt-eat-faults-on-vmxoff-in-reboot-flows.patch queue-5.4/x86-reboot-force-all-cpus-to-exit-vmx-root-if-vmx-is-supported.patch