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KVM: VMX: Skip VMCLEAR logic during emergency reboots if CR4.VMXE=0

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Bail from vmx_emergency_disable() without processing the list of loaded
VMCSes if CR4.VMXE=0, i.e. if the CPU can't be post-VMXON.  It should be
impossible for the list to have entries if VMX is already disabled, and
even if that invariant doesn't hold, VMCLEAR will #UD anyways, i.e.
processing the list is pointless even if it somehow isn't empty.

Assuming no existing KVM bugs, this should be a glorified nop.  The
primary motivation for the change is to avoid having code that looks like
it does VMCLEAR, but then skips VMXON, which is nonsensical.

Suggested-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Link: https://lore.kernel.org/r/20230721201859.2307736-20-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2023-07-21 13:18:59 -07:00
parent 2e6b9bd49b
commit a788fbb763
1 changed files with 10 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
arch/x86/kvm/vmx/vmx.c
View File

@ -754,12 +754,20 @@ static void vmx_emergency_disable(void)
kvm_rebooting = true;
/*
* Note, CR4.VMXE can be _cleared_ in NMI context, but it can only be
* set in task context. If this races with VMX is disabled by an NMI,
* VMCLEAR and VMXOFF may #UD, but KVM will eat those faults due to
* kvm_rebooting set.
*/
if (!(__read_cr4() & X86_CR4_VMXE))
return;
list_for_each_entry(v, &per_cpu(loaded_vmcss_on_cpu, cpu),
loaded_vmcss_on_cpu_link)
vmcs_clear(v->vmcs);
if (__read_cr4() & X86_CR4_VMXE)
kvm_cpu_vmxoff();
kvm_cpu_vmxoff();
}
static void __loaded_vmcs_clear(void *arg)