From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Jan Beulich <JBeulich@suse.com>,
Paul Durrant <Paul.Durrant@citrix.com>,
Yu Zhang <yu.c.zhang@linux.intel.com>
Cc: Kevin Tian <kevin.tian@intel.com>,
"Keir (Xen.org)" <keir@xen.org>, "Tim (Xen.org)" <tim@xen.org>,
George Dunlap <George.Dunlap@citrix.com>,
"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>,
"zhiyuan.lv@intel.com" <zhiyuan.lv@intel.com>,
"jun.nakajima@intel.com" <jun.nakajima@intel.com>
Subject: Re: [PATCH 3/3] Add HVMOP to map guest ram with p2m_ioreq_server to an ioreq server
Date: Wed, 23 Mar 2016 10:37:17 +0000 [thread overview]
Message-ID: <56F271DD.4020909@citrix.com> (raw)
In-Reply-To: <56F26E7202000078000DF8AF@prv-mh.provo.novell.com>
On 23/03/16 09:22, Jan Beulich wrote:
>>>> On 22.03.16 at 18:51, <Paul.Durrant@citrix.com> wrote:
>>> From: George Dunlap [mailto:george.dunlap@citrix.com]
>>> Sent: 22 March 2016 17:27
>>> There's not much documentation in the code about how this is expected to
>>> be used.
>>>
>>> For instance, having separate flags seems to imply that you can
>>> independently select either read intercept, write intercept, or both;
>>> but [ept_]p2m_type_to_flags() seems to assume that READ_ACCESS implies
>>> WRITE_ACCESS. Do you plan to implement them separately in the future?
>>> If not, would it be better to make the interface an enum instead?
>>>
>>> At very least it should be documented that READ_ACCESS implies
>>> WRITE_ACCESS.
>> That's not true. If WRITE_ACCESS has not been requested then writes are
>> handled directly in Xen rather than being forwarded to the ioreq server. If
>> h/w were to allow pages to be marked write-only then we wouldn't need to do
>> that.
> At least on EPT iirc you can have write-only pages, due to there
> being both an R and a W bit.
W and WX pages in EPT cause a MISCONFIG. All other combinations however
are usable.
~Andrew
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next prev parent reply other threads:[~2016-03-23 10:37 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-16 12:22 [PATCH 3/3] Add HVMOP to map guest ram with p2m_ioreq_server to an ioreq server Yu Zhang
2016-03-22 17:26 ` George Dunlap
2016-03-22 17:51 ` Paul Durrant
2016-03-23 9:22 ` Jan Beulich
2016-03-23 9:44 ` Yu, Zhang
2016-03-23 10:10 ` Jan Beulich
2016-03-23 10:37 ` Andrew Cooper [this message]
2016-03-23 11:43 ` George Dunlap
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