On 25/11/2015 16:45, Bandan Das wrote:
> Haozhong Zhang <haozhong.zhang@xxxxxxxxx> writes:
>
>> This patch removes the vpid check when emulating nested invvpid
>> instruction of type all-contexts invalidation. The existing code is
>> incorrect because:
>> (1) According to Intel SDM Vol 3, Section "INVVPID - Invalidate
>> Translations Based on VPID", invvpid instruction does not check
>> vpid in the invvpid descriptor when its type is all-contexts
>> invalidation.
>
> But iirc isn't vpid=0 reserved for root mode ? I think we don't want
> L1 hypervisor to be able do a invvpid(0).
The instruction simply "invalidates all mappings tagged with all
non-zero VPIDs", which in our case is all L0 mappings tagged with vpid02.
Paolo
>> (2) According to the same document, invvpid of type all-contexts
>> invalidation does not require there is an active VMCS, so/and
>> get_vmcs12() in the existing code may result in a NULL-pointer
>> dereference. In practice, it can crash both KVM itself and L1
>> hypervisors that use invvpid (e.g. Xen).
>
> If that is the case, then just check if it's null and return without
> doing anything.
>
>> Signed-off-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx>
>> ---
>> arch/x86/kvm/vmx.c | 5 -----
>> 1 file changed, 5 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 87acc52..af823a3 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -7394,11 +7394,6 @@ static int handle_invvpid(struct kvm_vcpu *vcpu)
>>
>> switch (type) {
>> case VMX_VPID_EXTENT_ALL_CONTEXT:
>> - if (get_vmcs12(vcpu)->virtual_processor_id == 0) {
>> - nested_vmx_failValid(vcpu,
>> - VMXERR_INVALID_OPERAND_TO_INVEPT_INVVPID);
>> - return 1;
>> - }
>> __vmx_flush_tlb(vcpu, to_vmx(vcpu)->nested.vpid02);
>> nested_vmx_succeed(vcpu);
>> break;
>
> I also noticed a BUG() here in the default. It might be a good idea to replace
> it with a WARN.
>
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