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Date:   Wed, 1 Sep 2021 22:54:33 +0000
From:   Sean Christopherson <seanjc@google.com>
To:     Paolo Bonzini <pbonzini@redhat.com>
Cc:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        isaku.yamahata@intel.com, David Matlack <dmatlack@google.com>,
        peterx@redhat.com
Subject: Re: [PATCH 01/16] KVM: MMU: pass unadulterated gpa to
 direct_page_fault
Message-ID: <YTAEqXlvNOgY5hII@google.com>
References: <20210807134936.3083984-1-pbonzini@redhat.com>
 <20210807134936.3083984-2-pbonzini@redhat.com>
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On Sat, Aug 07, 2021, Paolo Bonzini wrote:
> Do not bother removing the low bits of the gpa.  This masking dates back
> to the very first commit of KVM but it is unnecessary---or even
> problematic, because the gpa is later used to fill in the MMIO page cache.

I don't disagree with the code change, but I don't see how stripping the offset
can be problematic for the MMIO page cache.  I assume you're referring to
handle_abnormal_pfn() -> vcpu_cache_mmio_info().  The "gva" is masked with
PAGE_MASK, i.e. the offset is stripped anyways.  And fundamentally, that cache
is tied to the granularity of the memslots, tracking the offset would be wrong.