From: "Woods, Brian" <Brian.Woods@amd.com>
To: Paul Durrant <paul.durrant@citrix.com>
Cc: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
"Woods, Brian" <Brian.Woods@amd.com>,
"Suthikulpanit, Suravee" <Suravee.Suthikulpanit@amd.com>
Subject: Re: [PATCH v3] amd-iommu: remove page merging code
Date: Tue, 4 Dec 2018 23:31:02 +0000 [thread overview]
Message-ID: <20181204233059.GA15167@amd.com> (raw)
In-Reply-To: <20181128095559.5101-1-paul.durrant@citrix.com>
On Wed, Nov 28, 2018 at 09:55:59AM +0000, Paul Durrant 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 unused by Xen, or by hardware
> before the domain starts running. (XSA-275 disabled the operation of the
> code after domain creation completes).
>
> With the page merging logic present in its current form there are no spare
> ignored bits in the PTE at all, but PV-IOMMU support will require at least
> one spare bit to track which PTEs are added by hypercall.
>
> This patch removes the code, freeing up the remaining PTE ignored bits
> for other use, including PV-IOMMU support, as well as significantly
> simplifying and shortening the source by ~170 lines. There may be some
> marginal performance cost (but none has been observed in manual testing
> with a passed-through NVIDIA GPU) since higher order mappings will now be
> ruled out until a mapping order parameter is passed to iommu_ops. That will
> be dealt with by a subsequent patch though.
>
> Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Brian Woods <brian.woods@amd.com>
--
Brian Woods
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next prev parent reply other threads:[~2018-12-04 23:31 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-28 9:55 [PATCH v3] amd-iommu: remove page merging code Paul Durrant
2018-11-28 10:41 ` Andrew Cooper
2018-12-03 10:27 ` Paul Durrant
2018-12-04 23:31 ` Woods, Brian [this message]
2018-12-05 8:50 ` Paul Durrant
2018-12-11 11:00 ` Paul Durrant
2018-12-11 11:22 ` Jan Beulich
2018-12-11 11:30 ` Paul Durrant
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