On 2017年08月16日 21:26, Radim Krčmář wrote:
> 2017-08-15 21:58-0400, Lan Tianyu:
>> These CR3 VMEXITs was introduced for platform without "unrestricted guest"
>> support. This is to set ept identity table to guest CR3 in guest real
>> mode because these platforms don't support ept real mode(CR0.PE and CR0.PG
>> must be set to 1). But these VMEXITs is redundant for platforms with
>> "unrestricted guest" support.
>>
>> Signed-off-by: Lan Tianyu <tianyu....@intel.com>
>> ---
>> arch/x86/kvm/vmx.c | 22 +++++++++++++---------
>> 1 file changed, 13 insertions(+), 9 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> @@ -4311,7 +4313,9 @@ static void vmx_set_cr3(struct kvm_vcpu *vcpu,
>> unsigned long cr3)
>> }
>>
>> vmx_flush_tlb(vcpu);
>> - vmcs_writel(GUEST_CR3, guest_cr3);
>> +
>> + if (!enable_unrestricted_guest || !enable_ept)
>> + vmcs_writel(GUEST_CR3, guest_cr3);
>
> This looks wrong -- it would prevent update GUEST_CR3 outside of
> non-root mode with enable_unrestricted_guest.
>
OK. Do you mean nest mode? I didn't consider that case.
I thought there were three cases here.
1) Shadow page mode(enable_ept=0)
2) ept mode without unrestricted guest mode
(ept=1, enable_unrestricted_guest = 0)
3) ept mode with unrestricted guest mode
(ept=1, enable_unrestricted_guest = 1)
>From my understanding, only (1) and (2) need to update guest cr3.
If nest mode is still needed to update guest CR3, we can add
is_guest_mode() in the if condition. Other choice is to just ignore
setting guest cr3 for case3. The condition maybe changed to
if (!(enable_unrestricted_guest && enable_ept))
vmcs_writel(GUEST_CR3, guest_cr3);
--
Best regards
Tianyu Lan
