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From: "Roger Pau Monné" <roger.pau@citrix.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
	Andrew Cooper <andrew.cooper3@citrix.com>, Wei Liu <wl@xen.org>,
	George Dunlap <george.dunlap@citrix.com>,
	Ian Jackson <iwj@xenproject.org>
Subject: Re: [PATCH v2 8/8] x86/PV: use get_unsafe() instead of copy_from_unsafe()
Date: Tue, 23 Feb 2021 12:59:22 +0100	[thread overview]
Message-ID: <YDTuGn8YWRrWlbS9@Air-de-Roger> (raw)
In-Reply-To: <0a59ae2f-448e-610d-e8a2-a7c3f9f3918f@suse.com>

On Wed, Feb 17, 2021 at 09:23:33AM +0100, Jan Beulich wrote:
> The former expands to a single (memory accessing) insn, which the latter
> does not guarantee. Yet we'd prefer to read consistent PTEs rather than
> risking a split read racing with an update done elsewhere.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

Albeit I wonder why the __builtin_constant_p check done in
copy_from_unsafe is not enough to take the get_unsafe_size branch in
there. Doesn't sizeof(l{1,2}_pgentry_t) qualify as a built time
constant?

Or the fact that n it's a parameter to an inline function hides this,
in which case the __builtin_constant_p is pointless?

Thanks, Roger.


  reply	other threads:[~2021-02-23 11:59 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 [this message]
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
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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