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From: "Jan Beulich" <JBeulich@suse.com>
To: Kevin Tian <kevin.tian@intel.com>
Cc: Jun Nakajima <jun.nakajima@intel.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Donald D Dugger <donald.d.dugger@intel.com>,
	Aravind Gopalakrishnan <aravind.gopalakrishnan@amd.com>,
	David Vrabel <david.vrabel@citrix.com>,
	Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
	Sherry Hurwitz <sherry.hurwitz@amd.com>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Subject: Re: [PATCHv2 1/3] x86/fpu: improve check for XSAVE* not writing FIP/FDP fields
Date: Wed, 24 Feb 2016 03:49:30 -0700	[thread overview]
Message-ID: <56CD98CA02000078000D58D3@prv-mh.provo.novell.com> (raw)
In-Reply-To: <AADFC41AFE54684AB9EE6CBC0274A5D15F7C93E0@SHSMSX101.ccr.corp.intel.com>

>>> On 24.02.16 at 11:37, <kevin.tian@intel.com> wrote:
> Sorry I didn't quite get the question here. Could anyone of you
> write down a standalone description of the problem then I can
> forward internally to confirm since my translation might be
> inaccurate here?

What we'd like to get formally stated is whether FIP is guaranteed
to be treated as 48-bit pointer, which upon loading/storing by
64-bit {F,}X{XSAVE,RSTOR} will get truncated/canonicalized. With
FDP being a full 64-bit pointer on Intel CPUs (but only a 48 bit one
on AMD ones), and both your and their manuals implicitly describing
both as full 64-bit fields, FIP potentially also being a full 64-bit field
on past, present, or future CPUs would render David's intended
code improvement unsafe.

Jan

  reply	other threads:[~2016-02-24 10:49 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-02-23 11:05 [PATCHv2 0/3] x86: workaround inability to fully restore FPU state David Vrabel
2016-02-23 11:05 ` [PATCHv2 1/3] x86/fpu: improve check for XSAVE* not writing FIP/FDP fields David Vrabel
2016-02-23 11:18   ` Andrew Cooper
2016-02-23 11:54     ` David Vrabel
2016-02-23 14:07       ` Jan Beulich
2016-02-23 14:59   ` Jan Beulich
2016-02-23 17:42     ` David Vrabel
2016-02-24  7:51       ` Jan Beulich
2016-02-24 10:37         ` Tian, Kevin
2016-02-24 10:49           ` Jan Beulich [this message]
2016-03-18 18:23             ` Lai, Paul C
2016-02-23 11:05 ` [PATCHv2 2/3] x86/fpu: Add a per-domain field to set the width of FIP/FDP David Vrabel
2016-02-23 11:10   ` Andrew Cooper
2016-02-23 11:53     ` David Vrabel
2016-02-23 15:24   ` Jan Beulich
2016-02-23 16:27     ` David Vrabel
2016-02-23 16:39       ` Jan Beulich
2016-02-23 11:05 ` [PATCHv2 3/3] x86/hvm: add HVM_PARAM_X87_FIP_WIDTH David Vrabel
2016-02-23 11:20   ` Andrew Cooper
2016-02-24 11:51     ` Wei Liu

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