linux-kernel - Re: [PATCH v11 02/13] KVM: X86: Don't track dirty for KVM_SET_[TSS_ADDR|IDENTITY_MAP

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Date:   Wed, 22 Jul 2020 17:29:40 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Andrew Jones <drjones@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v11 02/13] KVM: X86: Don't track dirty for
 KVM_SET_[TSS_ADDR|IDENTITY_MAP_ADDR]

On Wed, Jul 08, 2020 at 03:33:57PM -0400, Peter Xu wrote:
> Originally, we have three code paths that can dirty a page without
> vcpu context for X86:
> 
>   - init_rmode_identity_map
>   - init_rmode_tss
>   - kvmgt_rw_gpa
> 
> init_rmode_identity_map and init_rmode_tss will be setup on
> destination VM no matter what (and the guest cannot even see them), so
> it does not make sense to track them at all.
> 
> To do this, allow __x86_set_memory_region() to return the userspace
> address that just allocated to the caller.  Then in both of the
> functions we directly write to the userspace address instead of
> calling kvm_write_*() APIs.
> 
> Another trivial change is that we don't need to explicitly clear the
> identity page table root in init_rmode_identity_map() because no
> matter what we'll write to the whole page with 4M huge page entries.
> 
> Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---

Reviewed-by: Sean Christopherson <sean.j.christopherson@...el.com>