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From: Jan Beulich <jbeulich@suse.com>
To: Andrew Cooper <amc96@srcf.net>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: "Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Wei Liu" <wl@xen.org>, "Roger Pau Monné" <roger.pau@citrix.com>,
	"Paul Durrant" <paul@xen.org>
Subject: Re: [PATCH 1/3] x86/HVM: permit CLFLUSH{,OPT} on execute-only code segments
Date: Fri, 3 Dec 2021 12:55:58 +0100	[thread overview]
Message-ID: <bb2f1d15-199c-b7d9-5a3e-70563e927cbf@suse.com> (raw)
In-Reply-To: <c375875f-0a21-e02b-6a2b-63ab91451373@srcf.net>

On 03.12.2021 12:48, Andrew Cooper wrote:
> On 03/12/2021 11:21, Jan Beulich wrote:
>> The SDM explicitly permits this, and since that's sensible behavior
>> don't special case AMD (where the PM doesn't explicitly say so).
> 
> APM explicitly says so too.
> 
> "The CLFLUSH instruction executes at any privilege level. CLFLUSH
> performs all the segmentation and paging checks that a 1-byte read would
> perform, except that it also allows references to execute-only segments."
> 
> and
> 
> "The CLFLUSHOPT instruction executes at any privilege level. CLFLUSHOPT
> performs all the segmentation and paging checks that a 1-byte read would
> perform, except that it also allows references to execute-only segments."

Somehow I didn't read further after the page table related paragraph,
perhaps on the assumption that like in the SDM it would be all in one
paragraph.

>> Fixes: 52dba7bd0b36 ("x86emul: generalize wbinvd() hook")
>> Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> 
> With the commit message tweaked, Reviewed-by: Andrew Cooper
> <andrew.cooper3@citrix.com>.  Far less invasive than I was fearing.

Thanks. I've switched to simply saying "Both SDM and PM explicitly
permit this."

Jan



  reply	other threads:[~2021-12-03 11:56 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-03 11:18 [PATCH 0/3] x86: insn-fetch related emulation adjustments Jan Beulich
2021-12-03 11:21 ` [PATCH 1/3] x86/HVM: permit CLFLUSH{,OPT} on execute-only code segments Jan Beulich
2021-12-03 11:48   ` Andrew Cooper
2021-12-03 11:55     ` Jan Beulich [this message]
2021-12-10 12:53   ` Durrant, Paul
2021-12-03 11:22 ` [PATCH 2/3] x86/HVM: fail virt-to-linear conversion for insn fetches from non-code segments Jan Beulich
2021-12-03 11:49   ` Andrew Cooper
2021-12-03 11:23 ` [PATCH 3/3] x86emul: drop "seg" parameter from insn_fetch() hook Jan Beulich
2021-12-03 12:24   ` Andrew Cooper
2021-12-10 12:56   ` Durrant, Paul
2021-12-10  9:43 ` Ping: [PATCH 0/3] x86: insn-fetch related emulation adjustments Jan Beulich

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