linux-kernel - Re: [PATCH v7 04/11] KVM: pfncache: base offset check on khva rather than gpa

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Message-ID: <ZUGQhfH3HE-y6_5C@google.com>
Date:   Tue, 31 Oct 2023 16:40:53 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paul Durrant <paul@....org>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Paul Durrant <pdurrant@...zon.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        David Woodhouse <dwmw2@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v7 04/11] KVM: pfncache: base offset check on khva rather
 than gpa

On Mon, Oct 02, 2023, Paul Durrant wrote:
> From: Paul Durrant <pdurrant@...zon.com>
> 
> After a subsequent patch, the gpa may not always be set whereas khva will
> (as long as the cache valid flag is also set).

This holds true only because there are no users of KVM_GUEST_USES_PFN, and
because hva_to_pfn_retry() rather oddly adds the offset to a NULL khva.

I think it's time to admit using this to map PFNs into the guest is a bad idea
and rip out KVM_GUEST_USES_PFN before fully relying on khva.

https://lore.kernel.org/all/ZQiR8IpqOZrOpzHC@google.com