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From: Paul Durrant <xadimgnik@gmail.com>
Message-ID: <a80b46a2-d07a-466e-b2b3-bed685292e47@xen.org>
Date: Thu, 21 Mar 2024 11:07:50 +0000
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Subject: Re: [PATCH 1/3] KVM: Add helpers to consolidate gfn_to_pfn_cache's
 page split check
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To: Sean Christopherson <seanjc@google.com>,
 Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
 syzbot+106a4f72b0474e1d1b33@syzkaller.appspotmail.com,
 David Woodhouse <dwmw2@infradead.org>
References: <20240320001542.3203871-1-seanjc@google.com>
 <20240320001542.3203871-2-seanjc@google.com>
Organization: Xen Project
In-Reply-To: <20240320001542.3203871-2-seanjc@google.com>
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On 20/03/2024 00:15, Sean Christopherson wrote:
> Add a helper to check that the incoming length for a gfn_to_pfn_cache is
> valid with respect to the cache's GPA and/or HVA.  To avoid activating a
> cache with a bogus GPA, a future fix will fork the page split check in
> the inner refresh path into activate() and the public rerfresh() APIs, at

nit: typo

> which point KVM will check the length in three separate places.
> 
> Deliberately keep the "page offset" logic open coded, as the only other
> path that consumes the offset, __kvm_gpc_refresh(), already needs to
> differentiate between GPA-based and HVA-based caches, and it's not obvious
> that using a helper is a net positive in overall code readability.
> 
> Note, for GPA-based caches, this has a subtle side effect of using the GPA
> instead of the resolved HVA in the check() path, but that should be a nop
> as the HVA offset is derived from the GPA, i.e. the two offsets are
> identical, barring a KVM bug.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>   virt/kvm/pfncache.c | 27 +++++++++++++++++++--------
>   1 file changed, 19 insertions(+), 8 deletions(-)
> 

Reviewed-by: Paul Durrant <paul@xen.org>