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Thu, 3 Jun 2021 20:11:52 +0000 Subject: Re: [PATCH v3 01/11] xen/manage: keep track of the on-going suspend mode To: Anchal Agarwal Cc: "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "hpa@zytor.com" , "jgross@suse.com" , "linux-pm@vger.kernel.org" , "linux-mm@kvack.org" , "sstabellini@kernel.org" , "konrad.wilk@oracle.com" , "roger.pau@citrix.com" , "axboe@kernel.dk" , "davem@davemloft.net" , "rjw@rjwysocki.net" , "len.brown@intel.com" , "pavel@ucw.cz" , "peterz@infradead.org" , "xen-devel@lists.xenproject.org" , "vkuznets@redhat.com" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "dwmw@amazon.co.uk" References: <20200925222826.GA11755@dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com> <20200930212944.GA3138@dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com> <8cd59d9c-36b1-21cf-e59f-40c5c20c65f8@oracle.com> <20210521052650.GA19056@dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com> <0b1f0772-d1b1-0e59-8e99-368e54d40fbf@oracle.com> <20210526044038.GA16226@dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com> <33380567-f86c-5d85-a79e-c1cd889f8ec2@oracle.com> <20210528215008.GA19622@dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com> <1ff91b30-3963-728e-aefb-57944197bdde@oracle.com> <20210602193743.GA28861@dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com> From: Boris Ostrovsky Message-ID: <2cb71322-9d3d-395e-293b-24888f5be759@oracle.com> Date: Thu, 3 Jun 2021 16:11:46 -0400 User-Agent: Mozilla/5.0 (Macintosh; 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dkim=pass header.d=oracle.com header.s=corp-2020-01-29 header.b=nAgUjNuo; dkim=pass header.d=oracle.onmicrosoft.com header.s=selector2-oracle-onmicrosoft-com header.b="yl/FOAbV"; dmarc=pass (policy=none) header.from=oracle.com; spf=none (imf09.hostedemail.com: domain of boris.ostrovsky@oracle.com has no SPF policy when checking 141.146.126.79) smtp.mailfrom=boris.ostrovsky@oracle.com X-Rspamd-Server: rspam03 X-Stat-Signature: dtq95i6dxjbp3gtajht5qe5obmrjw4h5 X-HE-Tag: 1622751131-724119 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000235, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 6/2/21 3:37 PM, Anchal Agarwal wrote: > On Tue, Jun 01, 2021 at 10:18:36AM -0400, Boris Ostrovsky wrote: >> > The resume won't fail because in the image the xen_vcpu and xen_vcpu_in= fo are > same. These are the same values that got in there during saving of the > hibernation image. So whatever xen_vcpu got as a value during boot time= registration on resume is > essentially lost once the jump into the saved kernel image happens. Int= eresting > part is if KASLR is not enabled boot time vcpup mfn is same as in the i= mage. Do you start the your guest right after you've hibernated it? What happen= s if you create (and keep running) a few other guests in-between? mfn wou= ld likely be different then I'd think. > Once you enable KASLR this value changes sometimes and whenever that ha= ppens > resume gets stuck. Does that make sense? > > No it does not resume successfully if hypercall fails because I was try= ing to > explicitly reset vcpu and invoke hypercall. > I am just wondering why does restore logic fails to work here or probab= ly I am > missing a critical piece here. If you are not using KASLR then xen_vcpu_info is at the same address ever= y time you boot. So whatever you registered before hibernating stays the = same when you boot second time and register again, and so successful comp= arison in xen_vcpu_setup() works. (Mostly by chance.) But if KASLR is on then this comparison not failing should cause xen_vcpu= pointer in the loaded image to become bogus because xen_vcpu is now regi= stered for a different xen_vcpu_info address during boot. >>> Another line of thought is something what kexec does to come around t= his problem >>> is to abuse soft_reset and issue it during syscore_resume or may be b= efore the image get loaded. >>> I haven't experimented with that yet as I am assuming there has to be= a way to re-register vcpus during resume. >> >> Right, that sounds like it should work. >> > You mean soft reset or re-register vcpu? Doing something along the lines of a soft reset. It should allow you to r= e-register. Not sure how you can use it without Xen changes though.=C2=A0 -boris