linux-kernel - Re: [PATCH 1/3] KVM: Add helpers to consolidate gfn_to_pfn

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Message-ID: <a80b46a2-d07a-466e-b2b3-bed685292e47@xen.org>
Date: Thu, 21 Mar 2024 11:07:50 +0000
From: Paul Durrant <xadimgnik@...il.com>
To: Sean Christopherson <seanjc@...gle.com>,
 Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 syzbot+106a4f72b0474e1d1b33@...kaller.appspotmail.com,
 David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH 1/3] KVM: Add helpers to consolidate gfn_to_pfn_cache's
 page split check

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@...gle.com>
> ---
>   virt/kvm/pfncache.c | 27 +++++++++++++++++++--------
>   1 file changed, 19 insertions(+), 8 deletions(-)
> 

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