Re: [PATCH 04/16] KVM: x86/mmu: Add address conversion functions for TDX shared bit of GPA

Huang, Kai
2024-05-16T01:40:53Z

On 16/05/2024 1:20 pm, Edgecombe, Rick P wrote:
> On Thu, 2024-05-16 at 13:04 +1200, Huang, Kai wrote:
>>
>> I really don't see difference between ...
>>
>>         is_private_mem(gpa)
>>
>> ... and
>>
>>         is_private_gpa(gpa)
>>
>> If it confuses me, it can confuses other people.
>
> Again, point taken. I'll try to think of a better name. Please share if you do.
>
>>
>> The point is there's really no need to distinguish the two.  The GPA is
>> only meaningful when it refers to the memory that it points to.
>>
>> So far I am not convinced we need this helper, because such info we can
>> already get from:
>>
>>    1) fault->is_private;
>>    2) Xarray which records memtype for given GFN.
>>
>> So we should just get rid of it.
>
> Kai, can you got look through the dev branch a bit more before making the same
> point on every patch?
>
> kvm_is_private_gpa() is used to set PFERR_PRIVATE_ACCESS, which in turn sets
> fault->is_private. So you are saying we can use these other things that are
> dependent on it. Look at the other callers too.

Well, I think I didn't make myself clear.

I don't object to have this helper. If it helps, then we can have it.

My objection is the current implementation of it, because it is
*conceptually* wrong for SEV-SNP.

Btw, I just look at the dev branch.

For the common code, it is used in kvm_tdp_mmu_map() and
kvm_tdp_mmu_fast_pf_get_last_sptep() to get whether a GPA is private.

As said above, I don't see why we need a helper with the "current
implementation" (which consults kvm_shared_gfn_mask()) for them. We can
just use fault->gfn + fault->is_private for such purpose.

It is also used in the TDX code like TDX variant handle_ept_violation()
and tdx_vcpu_init_mem_region(). For them to be honest I don't quite
care whether a helper is used. We can have a helper if we have multiple
callers, but this helper should be in TDX code, but not common MMU code.