linux-kernel - Re: [RFC PATCH 3/8] kvm: pfncache: enlighten about gmem

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Message-ID: <a232728115a94664c82a27ac78a2ae35bcdd3c37.camel@infradead.org>
Date: Wed, 10 Jul 2024 11:50:04 +0100
From: David Woodhouse <dwmw2@...radead.org>
To: Patrick Roy <roypat@...zon.co.uk>, seanjc@...gle.com,
 pbonzini@...hat.com,  akpm@...ux-foundation.org, rppt@...nel.org,
 david@...hat.com
Cc: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, 
 dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
 willy@...radead.org,  graf@...zon.com, derekmn@...zon.com,
 kalyazin@...zon.com, kvm@...r.kernel.org,  linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, dmatlack@...gle.com,  tabba@...gle.com,
 chao.p.peng@...ux.intel.com, xmarcalx@...zon.co.uk, James Gowans
 <jgowans@...zon.com>
Subject: Re: [RFC PATCH 3/8] kvm: pfncache: enlighten about gmem

On Wed, 2024-07-10 at 11:46 +0100, Patrick Roy wrote:
> On Wed, 2024-07-10 at 11:20 +0100, David Woodhouse wrote:
> > In that case, wouldn't that mean the explicit checks on gpc->is_private
> > matching kvm_mem_is_private() would be redundant and you can remove
> > them because you can trust that gpc->valid would be cleared?
> > 
> 
> Right, yes, it would indeed mean that. I'll double-check my assumption
> about the whole invalidation thing and adjust the code for the next
> iteration!

I was going to suggest that you take the check you'd added to
kvm_gpc_check() and move it down below the ->valid check, and turn it
into a BUG_ON() to check that assertion.

You *might* get false positives with that though, if the result of
kvm_mem_is_private() becomes true before the flush actually *happens*?

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