From: Jan Beulich <jbeulich@suse.com>
To: "Roger Pau Monné" <roger.pau@citrix.com>
Cc: xen-devel@lists.xenproject.org,
Jason Andryuk <jandryuk@gmail.com>,
Ian Jackson <ian.jackson@eu.citrix.com>, Wei Liu <wl@xen.org>,
Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [Xen-devel] [PATCH v2] x86/hvmloader: round up memory BAR size to 4K
Date: Tue, 21 Jan 2020 11:43:58 +0100 [thread overview]
Message-ID: <624c69b6-9a9d-7719-fdec-1c6e939a9f65@suse.com> (raw)
In-Reply-To: <20200121102941.GH11756@Air-de-Roger>
On 21.01.2020 11:29, Roger Pau Monné wrote:
> So I'm not sure how to progress with this patch, are we fine with
> those limitations?
I'm afraid this depends on ...
> As I said, Xen hasn't got enough knowledge to correctly isolate the
> BARs, and hence we have to rely on dom0 DTRT. We could add checks in
> Xen to make sure no BARs share a page, but it's a non-trivial amount
> of scanning and sizing each possible BAR on the system.
... whether Dom0 actually "DTRT", which in turn is complicated by there
not being a specific Dom0 kernel incarnation to check against. Perhaps
rather than having Xen check _all_ BARs, Xen or the tool stack could
check BARs of devices about to be handed to a guest? Perhaps we need to
pass auxiliary information to hvmloader to be able to judge whether a
BAR shares a page with another one? Perhaps there also needs to be a
way for hvmloader to know what offset into a page has to be maintained
for any particular BAR, as follows from Jason's recent reply?
> IMO this patch is an improvement over the current state, and we can
> always do further improvements afterwards.
As said, to me it looks as if it was breaking one case in order to fix
another. If I'm not wrong with this, I don't see how the patch is an
improvement.
Jan
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next prev parent reply other threads:[~2020-01-21 10:44 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-17 11:08 [Xen-devel] [PATCH v2] x86/hvmloader: round up memory BAR size to 4K Roger Pau Monne
2020-01-17 16:05 ` Jason Andryuk
2020-01-20 16:10 ` Jan Beulich
2020-01-20 17:18 ` Roger Pau Monné
2020-01-20 20:48 ` Jason Andryuk
2020-01-21 9:18 ` Jan Beulich
2020-01-21 10:29 ` Roger Pau Monné
2020-01-21 10:43 ` Jan Beulich [this message]
2020-01-21 15:57 ` Roger Pau Monné
2020-01-21 16:15 ` Jan Beulich
2020-01-21 16:57 ` Roger Pau Monné
2020-01-22 10:27 ` Jan Beulich
2020-01-22 10:51 ` Roger Pau Monné
2020-01-22 14:04 ` Jason Andryuk
2020-01-22 14:15 ` Jan Beulich
2020-01-22 14:12 ` Jan Beulich
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