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[54.240.197.224]) by smtp.gmail.com with ESMTPSA id f12sm7179254wmf.26.2020.10.01.01.50.56 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 01 Oct 2020 01:50:57 -0700 (PDT) From: Paul Durrant X-Google-Original-From: "Paul Durrant" Reply-To: To: "'Jan Beulich'" , "'Julien Grall'" Cc: "'Oleksandr'" , , "'Oleksandr Tyshchenko'" , "'Andrew Cooper'" , "'George Dunlap'" , "'Ian Jackson'" , "'Stefano Stabellini'" , "'Wei Liu'" , =?utf-8?Q?'Roger_Pau_Monn=C3=A9'?= , "'Jun Nakajima'" , "'Kevin Tian'" , "'Tim Deegan'" , "'Julien Grall'" References: <1599769330-17656-1-git-send-email-olekstysh@gmail.com> <1599769330-17656-3-git-send-email-olekstysh@gmail.com> <3997a705-ccb1-4b8f-41ca-c5507360c759@xen.org> <000201d69314$97bd8fa0$c738aee0$@xen.org> <2cbe7efd-f356-0f1b-0bb1-bfb2243f180c@xen.org> <0f768df9-6e28-a0ed-92e7-b17303c24996@suse.com> In-Reply-To: <0f768df9-6e28-a0ed-92e7-b17303c24996@suse.com> Subject: RE: [PATCH V1 02/16] xen/ioreq: Make x86's IOREQ feature common Date: Thu, 1 Oct 2020 09:50:55 +0100 Message-ID: <008d01d697cf$fac24b30$f046e190$@xen.org> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-Mailer: Microsoft Outlook 16.0 Content-Language: en-gb Thread-Index: AQIQ4beZ3sUmYihKXwfoVgy4BRIJGwHfeJxHAedMvHMBMIgdOgK34vRDAgTQpPsBrefRNqiyzR4g > -----Original Message----- > From: Jan Beulich > Sent: 01 October 2020 09:49 > To: Julien Grall > Cc: Oleksandr ; xen-devel@lists.xenproject.org; = paul@xen.org; 'Oleksandr > Tyshchenko' ; 'Andrew Cooper' = ; 'George > Dunlap' ; 'Ian Jackson' = ; 'Stefano Stabellini' > ; 'Wei Liu' ; 'Roger Pau = Monn=C3=A9' ; 'Jun > Nakajima' ; 'Kevin Tian' = ; 'Tim Deegan' ; > 'Julien Grall' > Subject: Re: [PATCH V1 02/16] xen/ioreq: Make x86's IOREQ feature = common >=20 > On 30.09.2020 19:47, Julien Grall wrote: > > Regarding the fix itself, I am not sure what sort of synchronization = we > > can do. Are you suggesting to wait for the I/O to complete? If so, = how > > do we handle the case the IOREQ server died? >=20 > In simple cases retrying the entire request may be an option. However, > if the server died after some parts of a multi-part operation were > done already, I guess the resulting loss of state is bad enough to > warrant crashing the guest. This shouldn't be much different from e.g. > a device disappearing from a bare metal system - any partial I/O done > to/from it will leave the machine in an unpredictable state, which it > may be too difficult to recover from without rebooting. (Of course, > staying with this analogue, it may also be okay to simple consider > the operation "complete", leaving it to the guest to recover. The > main issue on the hypervisor side then would be to ensure we don't > expose any uninitialized [due to not having got written to] data to > the guest.) >=20 I'll try to take a look today and come up with a patch. Paul