From: Jan Beulich <jbeulich@suse.com>
To: Ian Jackson <iwj@xenproject.org>
Cc: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
"Andrew Cooper" <andrew.cooper3@citrix.com>,
"Wei Liu" <wl@xen.org>, "Roger Pau Monné" <roger.pau@citrix.com>,
"George Dunlap" <george.dunlap@citrix.com>
Subject: Re: [PATCH v2 0/8] x86/PV: avoid speculation abuse through guest accessors
Date: Fri, 19 Feb 2021 17:16:55 +0100 [thread overview]
Message-ID: <fbac488e-383c-c5a9-585a-6609b81e7acc@suse.com> (raw)
In-Reply-To: <24623.58260.98531.223090@mariner.uk.xensource.com>
On 19.02.2021 17:13, Ian Jackson wrote:
> Jan Beulich writes ("Re: [PATCH v2 0/8] x86/PV: avoid speculation abuse through guest accessors"):
>> On 19.02.2021 16:50, Ian Jackson wrote:
>>> You say "consistency" but in practical terms, what will happen if the
>>> code is not "conxistent" in this sense ?
>>
>> Patches 4-6: The code is harder to understand with the mix of names.
>> Backports from future versions to 4.15 may require more attention to
>> get right (and then again the same level of attention when moving to
>> 4.14).
>>
>> Patches 7 is simply a minor improvement. Patch 8 is an equivalent
>> of the one patch of the earlier version which has already gone in.
>> Just like that other one it's more to avoid a latent issue than any
>> active one.
>
> Thank you for this clear explanation.
>
> I think 4-6 and 8 are good candidates for the reasons you give, and
> because they seem low risk to me. Have you used any automatic
> techniques to check that there is no unintentional codegen change ?
> (Eg, binary diffs, diffing sedderied versions, or something.)
I did some manual inspection at the time of putting together that
work, but nothing further to be honest.
> To my naive eye patch 7 looks scary because it might be moving the
> scope of a critical section. Am I wrong about that ?
At the source level it moves things, yes. Generated code, again as
per manual inspection, doesn't change, due to the pieces that the
compiler is able to eliminate. So I guess it's not as scary as it
may look.
Jan
next prev parent reply other threads:[~2021-02-19 16:17 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-17 8:16 [PATCH v2 0/8] x86/PV: avoid speculation abuse through guest accessors Jan Beulich
2021-02-17 8:19 ` [PATCH v2 1/8] x86: split __{get,put}_user() into "guest" and "unsafe" variants Jan Beulich
2021-02-17 8:20 ` [PATCH v2 2/8] x86: split __copy_{from,to}_user() " Jan Beulich
2021-02-17 8:20 ` [PATCH v2 3/8] x86/PV: harden guest memory accesses against speculative abuse Jan Beulich
2021-02-17 8:21 ` [PATCH v2 4/8] x86: rename {get,put}_user() to {get,put}_guest() Jan Beulich
2021-02-22 15:22 ` Roger Pau Monné
2021-02-17 8:21 ` [PATCH v2 5/8] x86/gdbsx: convert "user" to "guest" accesses Jan Beulich
2021-02-22 15:31 ` Roger Pau Monné
2021-02-22 15:55 ` Jan Beulich
2021-02-22 16:08 ` Roger Pau Monné
2021-02-17 8:22 ` [PATCH v2 6/8] x86: rename copy_{from,to}_user() to copy_{from,to}_guest_pv() Jan Beulich
2021-02-23 11:04 ` Roger Pau Monné
2021-02-23 15:15 ` Jan Beulich
2021-02-17 8:22 ` [PATCH v2 7/8] x86: move stac()/clac() from {get,put}_unsafe_asm() Jan Beulich
2021-02-23 11:40 ` Roger Pau Monné
2021-02-17 8:23 ` [PATCH v2 8/8] x86/PV: use get_unsafe() instead of copy_from_unsafe() Jan Beulich
2021-02-23 11:59 ` Roger Pau Monné
2021-02-23 15:25 ` Jan Beulich
2021-02-23 15:37 ` Roger Pau Monné
2021-02-23 16:13 ` Jan Beulich
2021-02-23 18:03 ` Roger Pau Monné
2021-02-19 15:50 ` [PATCH v2 0/8] x86/PV: avoid speculation abuse through guest accessors Ian Jackson
2021-02-19 15:56 ` Jan Beulich
2021-02-19 16:13 ` Ian Jackson
2021-02-19 16:16 ` Jan Beulich [this message]
2021-02-19 16:30 ` Ian Jackson
2021-02-24 11:13 ` Jan Beulich
2021-02-24 13:08 ` Ian Jackson
2021-02-24 13:18 ` Jan Beulich
2021-02-24 13:26 ` Ian Jackson
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