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From: "Jan Beulich" <JBeulich@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: xen-devel <xen-devel@lists.xenproject.org>,
	Paul Durrant <paul.durrant@citrix.com>,
	Brian Woods <brian.woods@amd.com>,
	Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Subject: Re: [PATCH] amd-iommu: remove page merging code
Date: Tue, 27 Nov 2018 08:42:57 -0700	[thread overview]
Message-ID: <5BFD660102000078002006FB@prv1-mh.provo.novell.com> (raw)
In-Reply-To: <a500cc7c-ec6b-9894-63a0-df3329790bdc@citrix.com>

>>> On 27.11.18 at 15:19, <andrew.cooper3@citrix.com> wrote:
> On 27/11/2018 13:06, Jan Beulich wrote:
>>>>> On 26.11.18 at 18:30, <paul.durrant@citrix.com> wrote:
>>> The page merging logic makes use of bits 1-8 and bit 63 of a PTE, which used
>>> to be specified as ignored. However, bits 5 and 6 are now specified as
>>> 'accessed' and 'dirty' bits and their use only remains safe as long as
>>> the DTE 'Host Access Dirty' bits remain clear.
>> Upon second thought - is this actually true with the XSA-275
>> changes in place? As long as the domain is not running yet,
>> how would A and/or D bits get set?
> 
> DTE.HAD is an IOMMU control which Xen doesn't currently enable, so this
> isn't an issue in current usage.

Well, of course, and Paul did say so. My point is that even when we
start using the feature, as long as we don't set A and/or D bits
ourselves, nothing is getting in the way of the merging code, as it
ceases to do anything once the domain starts running.

Jan



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  parent reply	other threads:[~2018-11-27 15:43 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-26 17:30 [PATCH] amd-iommu: remove page merging code Paul Durrant
2018-11-27 13:01 ` Jan Beulich
2018-11-27 14:12   ` Paul Durrant
2018-11-27 15:48     ` Jan Beulich
2018-11-27 13:06 ` Jan Beulich
2018-11-27 14:19   ` Andrew Cooper
2018-11-27 14:21     ` Paul Durrant
2018-11-27 15:42     ` Jan Beulich [this message]
2018-11-27 14:20   ` Paul Durrant
2018-11-27 15:50     ` Jan Beulich
2018-11-27 15:57       ` Paul Durrant

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