From: "Roger Pau Monné" <roger.pau@citrix.com>
To: Jan Beulich <jbeulich@suse.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: Mon, 20 Jan 2020 17:18:40 +0000 [thread overview]
Message-ID: <20200120171840.GF11756@Air-de-Roger> (raw)
In-Reply-To: <538864f7-f537-be0d-e37b-8f29baf82ee0@suse.com>
On Mon, Jan 20, 2020 at 05:10:33PM +0100, Jan Beulich wrote:
> On 17.01.2020 12:08, Roger Pau Monne wrote:
> > When placing memory BARs with sizes smaller than 4K multiple memory
> > BARs can end up mapped to the same guest physical address, and thus
> > won't work correctly.
>
> Thinking about it again, aren't you fixing one possible case by
> breaking the opposite one: What you fix is when the two distinct
> BARs (of the same or different devices) map to distinct MFNs
> (which would have required a single GFN to map to both of these
> MFNs). But don't you, at the same time, break the case of two
> BARs (perhaps, but not necessarily, of the same physical device)
> mapping both to the same MFN, i.e. requiring to have two distinct
> GFNs map to one MFN? (At least for the moment I can't see a way
> for hvmloader to distinguish the two cases.)
IMO we should force all BARs to be page-isolated by dom0 (since Xen
doesn't have the knowledge of doing so), but I don't see the issue
with having different gfns pointing to the same mfn. Is that a
limitation of paging? I think you can map a grant multiple times into
different gfns, which achieves the same AFAICT.
Roger.
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next prev parent reply other threads:[~2020-01-20 17:19 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 [this message]
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
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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