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Date: Fri, 30 Dec 2022 17:19:49 +0200
From: Mike Rapoport <rppt@kernel.org>
To: Borislav Petkov <bp@alien8.de>
Cc: Michael Roth <michael.roth@amd.com>,
	Ashish Kalra <Ashish.Kalra@amd.com>, x86@kernel.org,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	linux-coco@lists.linux.dev, linux-mm@kvack.org,
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	vkuznets@redhat.com, jmattson@google.com, luto@kernel.org,
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	peterz@infradead.org, srinivas.pandruvada@linux.intel.com,
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	dgilbert@redhat.com, jarkko@kernel.org
Subject: Re: [PATCH Part2 v6 07/49] x86/sev: Invalid pages from direct map
 when adding it to RMP table
Message-ID: <Y68BlcnT0vrpcwf5@kernel.org>
References: <cover.1655761627.git.ashish.kalra@amd.com>
 <243778c282cd55a554af9c11d2ecd3ff9ea6820f.1655761627.git.ashish.kalra@amd.com>
 <YuFvbm/Zck9Tr5pq@zn.tnic>
 <20221219150026.bltiyk72pmdc2ic3@amd.com>
 <Y6DEv4QuvIfwWlCW@zn.tnic>
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In-Reply-To: <Y6DEv4QuvIfwWlCW@zn.tnic>

On Mon, Dec 19, 2022 at 09:08:31PM +0100, Borislav Petkov wrote:
> On Mon, Dec 19, 2022 at 09:00:26AM -0600, Michael Roth wrote:
> > We implemented this approach for v7, but it causes a fairly significant
> > performance regression, particularly for the case for npages > 1 which
> > this change was meant to optimize.
> > 
> > I still need to dig in a big but I'm guessing it's related to flushing
> > behavior.
> 
> Well, AFAICT, change_page_attr_set_clr() flushes once at the end.
> 
> Don't you need to flush when you modify the direct map?
> 
> > It would however be nice to have a set_direct_map_default_noflush()
> > variant that accepted a 'npages' argument, since it would be more
> > performant here and also would potentially allow for restoring the 2M
> > direct mapping in some cases. Will look into this more for v8.
> 
> set_pages_direct_map_default_noflush()
>
> I guess.
> 
> Although the name is a mouthful so I wouldn't mind having those
> shortened.

I had a patch that just adds numpages parameter:

https://lore.kernel.org/lkml/20201123095432.5860-4-rppt@kernel.org/

The set_direct_map*() are not too widely used, so it's not a big deal to
update all callers.
 
> In any case, as long as that helper is properly defined and documented,
> I don't mind.
> 
> Thx.
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette
> 

-- 
Sincerely yours,
Mike.