Re: [PATCH 2/3] KVM: x86: let reexecute_instruction work for tdp

Xiao Guangrong
2012-11-27T03:13:24Z

On 11/27/2012 06:37 AM, Marcelo Tosatti wrote:
> On Tue, Nov 20, 2012 at 07:59:10AM +0800, Xiao Guangrong wrote:
>> Currently, reexecute_instruction refused to retry all instructions. If
>> nested npt is used, the emulation may be caused by shadow page, it can
>> be fixed by dropping the shadow page
>>
>> Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
>> ---
>> arch/x86/kvm/x86.c | 14 ++++++++------
>> 1 files changed, 8 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 7be8452..5fe72cc 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -4469,17 +4469,19 @@ static int handle_emulation_failure(struct kvm_vcpu *vcpu)
>> return r;
>> }
>>
>> -static bool reexecute_instruction(struct kvm_vcpu *vcpu, gva_t gva)
>> +static bool reexecute_instruction(struct kvm_vcpu *vcpu, unsigned long cr2)
>> {
>> - gpa_t gpa;
>> + gpa_t gpa = cr2;
>> pfn_t pfn;
>>
>> - if (tdp_enabled)
>> + if (!ACCESS_ONCE(vcpu->kvm->arch.indirect_shadow_pages))
>> return false;
>
> How is indirect_shadow_pages protected? Why is ACCESS_ONCE() being used
> to read it?

Hi Marcelo,

It is protected by mmu-lock for it only be changed when mmu-lock is hold. And
ACCESS_ONCE is used on read path avoiding magic optimization from compiler.