From: Tim Deegan <tim@xen.org>
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>, "Roger Pau Monné" <roger.pau@citrix.com>,
"George Dunlap" <george.dunlap@citrix.com>
Subject: Re: [PATCH 15/17] x86/shadow: drop SH_type_l2h_pae_shadow
Date: Fri, 22 Jan 2021 20:02:29 +0000 [thread overview]
Message-ID: <YAsvVUUqSQ9bUK32@deinos.phlegethon.org> (raw)
In-Reply-To: <c8de294c-ae72-aebf-a893-790c84efdc97@suse.com>
Hi,
At 17:31 +0100 on 22 Jan (1611336662), Jan Beulich wrote:
> On 22.01.2021 14:11, Tim Deegan wrote:
> > At 16:10 +0100 on 14 Jan (1610640627), Jan Beulich wrote:
> >> hash_{domain,vcpu}_foreach() have a use each of literal 15. It's not
> >> clear to me what the proper replacement constant would be, as it
> >> doesn't look as if SH_type_monitor_table was meant.
> >
> > Good spot. I think the '<= 15' should be replaced with '< SH_type_unused'.
> > It originally matched the callback arrays all being coded as
> > "static hash_callback_t callbacks[16]".
>
> So are you saying this was off by one then prior to this patch
> (when SH_type_unused was still 17), albeit in apparently a
> benign way?
Yes - this assertion is just to catch overruns of the callback table,
and so it was OK for its limit to be too low. The new types that were
added since then are never put in the hash table, so don't trigger
this assertion.
> And the comments in sh_remove_write_access(),
> sh_remove_all_mappings(), sh_remove_shadows(), and
> sh_reset_l3_up_pointers() are then wrong as well, and would
> instead better be like in shadow_audit_tables()?
Yes, it looks like those comments are also out of date where they
mention 'unused'.
> Because of this having been benign (due to none of the callback
> tables specifying non-NULL entries there), wouldn't it make
> sense to dimension the tables by SH_type_max_shadow + 1 only?
> Or would you consider this too risky?
Yes, I think that would be fine, also changing '<= 15' to
'<= SH_type_max_shadow'. Maybe add a matching
ASSERT(t <= SH_type_max_shadow) in shadow_hash_insert as well?
Cheers,
Tim.
next prev parent reply other threads:[~2021-01-22 20:02 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-14 15:01 [PATCH 00/17] x86/PV: avoid speculation abuse through guest accessors plus Jan Beulich
2021-01-14 15:03 ` [PATCH 01/17] x86/shadow: use __put_user() instead of __copy_to_user() Jan Beulich
2021-01-14 15:04 ` [PATCH 02/17] x86: split __{get,put}_user() into "guest" and "unsafe" variants Jan Beulich
2021-02-05 15:43 ` Roger Pau Monné
2021-02-05 16:13 ` Jan Beulich
2021-02-05 16:18 ` Roger Pau Monné
2021-02-05 16:26 ` Jan Beulich
2021-02-09 13:07 ` Roger Pau Monné
2021-02-09 13:15 ` Jan Beulich
2021-02-09 14:46 ` Roger Pau Monné
2021-02-09 14:57 ` Jan Beulich
2021-02-09 15:23 ` Roger Pau Monné
2021-02-09 14:55 ` Roger Pau Monné
2021-02-09 15:14 ` Jan Beulich
2021-02-09 15:27 ` Roger Pau Monné
2021-01-14 15:04 ` [PATCH 03/17] x86: split __copy_{from,to}_user() " Jan Beulich
2021-02-09 16:06 ` Roger Pau Monné
2021-02-09 17:03 ` Jan Beulich
2021-01-14 15:04 ` [PATCH 04/17] x86/PV: harden guest memory accesses against speculative abuse Jan Beulich
2021-02-09 16:26 ` Roger Pau Monné
2021-02-10 16:55 ` Jan Beulich
2021-02-11 8:11 ` Roger Pau Monné
2021-02-11 11:28 ` Jan Beulich
2021-02-12 10:41 ` Roger Pau Monné
2021-02-12 12:48 ` Jan Beulich
2021-02-12 13:02 ` Roger Pau Monné
2021-02-12 13:15 ` Jan Beulich
2021-01-14 15:05 ` [PATCH 05/17] x86: rename {get,put}_user() to {get,put}_guest() Jan Beulich
2021-01-14 15:05 ` [PATCH 06/17] x86/gdbsx: convert "user" to "guest" accesses Jan Beulich
2021-01-14 15:06 ` [PATCH 07/17] x86: rename copy_{from,to}_user() to copy_{from,to}_guest_pv() Jan Beulich
2021-01-14 15:07 ` [PATCH 08/17] x86: move stac()/clac() from {get,put}_unsafe_asm() Jan Beulich
2021-01-14 15:07 ` [PATCH 09/17] x86/PV: use get_unsafe() instead of copy_from_unsafe() Jan Beulich
2021-01-14 15:08 ` [PATCH 10/17] x86/shadow: " Jan Beulich
2021-01-14 15:08 ` [PATCH 11/17] x86/shadow: polish shadow_write_entries() Jan Beulich
2021-01-14 15:09 ` [PATCH 12/17] x86/shadow: move shadow_set_l<N>e() to their own source file Jan Beulich
2021-01-14 15:09 ` [PATCH 13/17] x86/shadow: don't open-code SHF_* shorthands Jan Beulich
2021-01-14 15:10 ` [PATCH 14/17] x86/shadow: SH_type_l2h_shadow is PV-only Jan Beulich
2021-01-14 15:10 ` [PATCH 15/17] x86/shadow: drop SH_type_l2h_pae_shadow Jan Beulich
2021-01-22 13:11 ` Tim Deegan
2021-01-22 16:31 ` Jan Beulich
2021-01-22 20:02 ` Tim Deegan [this message]
2021-01-25 11:09 ` Jan Beulich
2021-01-25 11:33 ` Jan Beulich
2021-01-14 15:10 ` [PATCH 16/17] x86/shadow: only 4-level guest code needs building when !HVM Jan Beulich
2021-01-14 15:11 ` [PATCH 17/17] x86/shadow: adjust is_pv_*() checks Jan Beulich
2021-01-22 13:18 ` [PATCH 00/17] x86/PV: avoid speculation abuse through guest accessors plus Tim Deegan
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