linux-kernel - Re: [PATCH v4 1/2] x86/arch_prctl: Fix the ARCH_REQ_XCOMP

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Date:   Tue, 8 Mar 2022 16:36:59 +0800
From:   Hao Xiang <hao.xiang@...ux.alibaba.com>
To:     "Chang S. Bae" <chang.seok.bae@...el.com>, yang.zhong@...el.com
Cc:     bp@...en8.de, dave.hansen@...ux.intel.com,
        linux-kernel@...r.kernel.org, mingo@...hat.com,
        ravi.v.shankar@...el.com, tglx@...utronix.de, x86@...nel.org
Subject: Re: [PATCH v4 1/2] x86/arch_prctl: Fix the ARCH_REQ_XCOMP_PERM
 implementation

Using the linux upsteam code with your patches，the problem is not 
reproduced. Maybe my patches are incomplete.

Thanks,
Hao

On 2022/3/8 2:53, Chang S. Bae wrote:
> On 3/7/2022 4:20 AM, Hao Xiang wrote:
>> x86/arch_prctl: Fix the ARCH_REQ_XCOMP_PERM implementation
>>
>> If WRITE_ONCE(perm->__state_perm, requested) is modified to
>> WRITE_ONCE(perm->__state_perm, mask), When the qemu process does not 
>> request the XFEATURE_MASK_XTILE_DATA xsave state permission, there may 
>> be a gp error (kvm: kvm_set_xcr line 1091 inject gp fault with cpl 0) 
>> because __kvm_set_xcr return 1.
> 
> What you said here does not make sense to me. When the Qemu process does 
> not request XTILEDATA, then the __xstate_request_perm() function is 
> never called in this, no?
> 
>>
>> static int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr){
>>      ...
>>      // xcr0 includes XFEATURE_MASK_XTILE_CFG by default.
>>      if ((xcr0 & XFEATURE_MASK_XTILE) &&
>>          ((xcr0 & XFEATURE_MASK_XTILE) != XFEATURE_MASK_XTILE))
>>          return 1;
>>      ...
>> }
>>
>> diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
>> index 02b3dda..2d4363e 100644
>> --- a/arch/x86/kernel/fpu/xstate.c
>> +++ b/arch/x86/kernel/fpu/xstate.c
>> @@ -1636,7 +1636,7 @@ static int __xstate_request_perm(u64 permitted, 
>> u64 requested, bool guest)
>>
>>          perm = guest ? &fpu->guest_perm : &fpu->perm;
>>          /* Pairs with the READ_ONCE() in xstate_get_group_perm() */
>> -       WRITE_ONCE(perm->__state_perm, requested);
>> +       WRITE_ONCE(perm->__state_perm, mask);
>>          /* Protected by sighand lock */
>>          perm->__state_size = ksize;
>>          perm->__user_state_size = usize;
>> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
>> index 494d4d3..e8704568 100644
>> --- a/arch/x86/kvm/cpuid.c
>> +++ b/arch/x86/kvm/cpuid.c
>> @@ -908,6 +908,9 @@ static inline int __do_cpuid_func(struct 
>> kvm_cpuid_array *array, u32 function)
>>                  break;
>>          case 0xd: {
>>                  u64 permitted_xcr0 = supported_xcr0 & 
>> xstate_get_guest_group_perm();
> 
> Yang, I think you should have included your fix [1] in your series [2] 
> in the first place, before using it widely like [3].
> 
>> +               permitted_xcr0 = ((permitted_xcr0 & 
>> XFEATURES_MASK_XTILE) != XFEATURES_MASK_XTILE)
>> +                               ? permitted_xcr0
>> +                               : permitted_xcr0 & ~XFEATURES_MASK_XTILE;
>>                  u64 permitted_xss = supported_xss;
>>
>>                  entry->eax &= permitted_xcr0;
>>
> 
> Well, first of all, one patch should fix one issue, not two or more, no?
> 
> But this hunk looks duplicate with this [4].
> 
> Thanks,
> Chang
> 
> 
> [1] 
> https://lore.kernel.org/lkml/20211108222815.4078-1-yang.zhong@intel.com/
> [2] 
> https://lore.kernel.org/lkml/20220105123532.12586-1-yang.zhong@intel.com/
> [3] 
> https://lore.kernel.org/lkml/20220105123532.12586-2-yang.zhong@intel.com/
> [4] 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x86/kvm/x86.c#n1033 
>