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Authentication-Results: esa6.hc3370-68.iphmx.com; dkim=none (message not signed) header.i=none IronPort-SDR: jXKgeqHSUaj2Qd6gHAaFfKACcooX+EHsCGXz7oEzrtTMBO+4tdCE0CkENe2rnuz1SX7NlfTkY3 Pc9tWDLMB5+0Q+hucFXjCus6peGk2+TJOTncPE/gGaGuoJeFQLNnpDRyN1eEz6n1txeQSKQ93z a0AGNTx+b6Y4zCdzw68npUQuMTayIc9Sa9NlbuesnVpr17s7POIfhP6iYeSO5g0n+5o80LDW4Z SnEJnut99v3CzOPK/sd+07X8LdbHoyL/ykMay7kamcox0F1RX7QElSmiMhI5+1TASc+1SLEFmy 6oY= X-SBRS: 2.5 X-MesageID: 29407124 X-Ironport-Server: esa6.hc3370-68.iphmx.com X-Remote-IP: 162.221.158.21 X-Policy: $RELAYED X-IronPort-AV: E=Sophos;i="5.77,382,1596513600"; d="scan'208";a="29407124" Subject: Re: [PATCH] x86/traps: 'Fix' safety of read_registers() in #DF path To: Jan Beulich CC: Xen-devel , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , Wei Liu , Julien Grall References: <20201012134908.27497-1-andrew.cooper3@citrix.com> <307753b0-fef8-658d-f897-8c0eb99ce3e5@citrix.com> <948f0753-561b-15e8-bf8c-52ff507133d2@suse.com> <00ba5885-5ee6-c772-a72e-15431cd3b1f4@suse.com> <09049e52-548b-3ffc-5259-b1ffc26413a5@citrix.com> <7f3272d5-8ec7-26ec-33ec-2281539920e2@suse.com> From: Andrew Cooper Message-ID: <5807e645-7242-125a-03cf-c7c23f28dfa3@citrix.com> Date: Fri, 16 Oct 2020 13:07:39 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <7f3272d5-8ec7-26ec-33ec-2281539920e2@suse.com> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Content-Language: en-GB X-ClientProxiedBy: AMSPEX02CAS02.citrite.net (10.69.22.113) To FTLPEX02CL05.citrite.net (10.13.108.178) On 16/10/2020 12:55, Jan Beulich wrote: > On 16.10.2020 13:24, Andrew Cooper wrote: >> On a tangent, what are your views WRT backport beyond 4.14? >> >> Back then, it was #DB which was adjacent to the guard frame (which was >> not present), but it doesn't use show_registers() by default, so I think >> the problem is mostly hidden. > I wasn't fully decided yet, but as long as it applies reasonably > cleanly I think I'm leaning towards also putting it on 4.13. > 4.12 closes anyway once 4.12.4 is out, and I don't think I want > to pick up not-really-urgent changes for putting there beyond > the few ones that I already have (and that I mean to put in > alongside the XSA fixes on Tuesday); I could be talked into it, > though. The question I was asking was really "should I try and make an equivalent fix for 4.13 and older". While the base premise of the fix would be the same, the logic in load_system_tables() is different, and the commit message is completely wrong. I only encountered this problem with added instrumentation in the #DB handler, which is why I'm questioning the utility of going to this effort. ~Andrew