Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [PATCH] Fix undefined operation VMXOFF during reboot and crash | Date | Thu, 11 Jun 2020 00:08:48 +0200 |
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Sean Christopherson <sean.j.christopherson@intel.com> writes: > Gah, I typed too slow :-)
Haha. I had the same thought.
> On Wed, Jun 10, 2020 at 11:34:21PM +0200, Thomas Gleixner wrote: >> We have exception fixups to avoid exactly that kind of horrible >> workarounds all over the place. >> >> static inline int cpu_vmxoff_safe(void) >> { >> int err; >> >> asm volatile("2: vmxoff; xor %[err],%[err]\n" >> "1:\n\t" >> ".section .fixup,\"ax\"\n\t" >> "3: mov %[fault],%[err] ; jmp 1b\n\t" >> ".previous\n\t" >> _ASM_EXTABLE(2b, 3b) >> : [err] "=a" (err) >> : [fault] "i" (-EFAULT) >> : "memory"); >> return err; >> } >> >> static inline void __cpu_emergency_vmxoff(void) >> { >> if (!cpu_vmx_enabled()) >> return; >> if (!cpu_vmxoff_safe()) >> cr4_clear_bits(X86_CR4_VMXE); > > This bit is wrong, CR4.VMXE should be cleared even if VMXOFF faults, e.g. > if this is called in NMI context and the NMI arrived in KVM code between > VMXOFF and clearing CR4.VMXE.
Oh, right.
> All other VMXOFF faults are mode related, i.e. any fault is guaranteed to > be due to the !post-VMXON check unless we're magically in RM, VM86, compat > mode, or at CPL>0.
Your patch is simpler indeed.
Thanks,
tglx
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