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d="scan'208";a="16454740" Subject: Re: [PATCH] tools/xenstore: don't store domU's mfn of ring page in xensotred To: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= , Julien Grall , Julien Grall References: <20200428155144.8253-1-jgross@suse.com> <76ed29d6-e2fc-cd48-6de7-e0032daaa2e9@xen.org> <3fd79cb1-e18f-1987-69ff-94f1bd15c66f@citrix.com> <3dcbe001-c66c-13a6-7a28-ef24b05eefa0@suse.com> <0f553a2e-9541-8d47-c354-0e8273b4b783@suse.com> From: Igor Druzhinin Message-ID: Date: Wed, 29 Apr 2020 14:39:12 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <0f553a2e-9541-8d47-c354-0e8273b4b783@suse.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: xen-devel , Paul Durrant , Ian Jackson , Wei Liu , "andrew.cooper3@citrix.com" Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On 29/04/2020 14:06, Jürgen Groß wrote: > On 29.04.20 14:49, Igor Druzhinin wrote: >> On 29/04/2020 13:29, Jürgen Groß wrote: >>> On 29.04.20 13:04, Igor Druzhinin wrote: >> >> Yes, XAPI is doing soft reset differently from libxl. You need to keep xenstore >> data to at least keep backends working without the need to reinitialize them >> before entering kdump kernel. We do the same thing while entering crash kernel >> in Windows after BSOD (CC Paul as he recommended this approach). >> There are other reasons to not reset xenstore data. >> >> I considered XS_INTRODUCE functionality to be part of xenstored ABI and we built >> a lot of infrastructure on top of that. So I don't think it could be easily removed now. > > Nobody wants to remove XS_INTRODUCE. It was just questioned there is a > need to call XS_INTRODUCE multiple times for a domain without a call of > XS_RELEASE in between. Sorry, I didn't mean the whole XS_INTRODUCE but that particular bit that allows it to rebind the channels without calling XS_RELEASE first as the latter has a lot of implications from toolstack point of view. > In case there is such a need this means we either should just drop the > test for the mfn to match and recreate the event-channel (which will do > no harm IMO), or we need to keep the mfn in the live-update state record > with the knowledge that it is far from being a good indicator for the > test whether a domain is known already or not (two HVM domains using a > similar configuration with the very same kernel will use the same gfn > probably). > > As only dom0 is allowed to use XS_INTRODUCE and I'm not aware of any > problems with neither XS_INTRODUCE failing due to illegal calls (no mfn > match), nor with potentially recreating the event channel for a "wrong" > domain, I suggest to just allow XS_INTRODUCE to be called as often as > the toolstack wants to. If that means keeping the current semantics of XS_INTRODUCE - I'd be quite happy with that. Igor