From: "Xia, Hongyan" <firstname.lastname@example.org> To: "email@example.com" <firstname.lastname@example.org>, "email@example.com" <firstname.lastname@example.org> Cc: "email@example.com" <firstname.lastname@example.org>, "email@example.com" <firstname.lastname@example.org>, "Gul, Mahircan" <email@example.com>, "firstname.lastname@example.org" <email@example.com>, "Ning, Raphael" <firstname.lastname@example.org>, "email@example.com" <firstname.lastname@example.org>, "email@example.com" <firstname.lastname@example.org>, "Grall, Julien" <email@example.com>, "firstname.lastname@example.org" <email@example.com>, "firstname.lastname@example.org" <email@example.com>, "firstname.lastname@example.org" <email@example.com> Subject: Re: [PATCH RFC 1/2] docs/design: Add a design document for Live Update Date: Fri, 7 May 2021 14:59:14 +0000 [thread overview] Message-ID: <firstname.lastname@example.org> (raw) In-Reply-To: <email@example.com> On Fri, 2021-05-07 at 14:15 +0200, Jan Beulich wrote: > On 07.05.2021 13:44, Julien Grall wrote: [...] > > > > It is a known convenient place. It may be difficult to find a > > similar > > spot on host that have been long-running. > > I'm not convinced: If it was placed in the kexec area at a 2Mb > boundary, it could just run from there. If the kexec area is > large enough, this would work any number of times (as occupied > ranges become available again when the next LU cycle ends). To make sure the next Xen can be loaded and run anywhere in case kexec cannot find large enough memory under 4G, we need to: 1. teach kexec to load the whole image contiguously. At the moment kexec prepares scattered 4K pages which are not runnable until they are copied to a contiguous destination. (What if it can't find a contiguous range?) 2. teach Xen that it can be jumped into with some existing page tables which point to itself above 4G. We can't do real/protected mode entry because it needs to start below 4G physically. Maybe a modified version of the EFI entry path (my familiarity with Xen EFI entry is limited)? 3. rewrite all the early boot bits that assume Xen is under 4G and its bundled page tables for below 4G. These are the obstacles off the top of my head. So I think there is no fundamental reason why we have to place Xen #2 where Xen #1 was, but doing so is a massive reduction of pain which allows us to reuse much of the existing Xen code. Maybe, this part does not have to be part of the ABI and we just suggest this as one way of loading the next Xen to cope with growth? This is the best way I can think of (loading Xen where it was and expand into the reserved bootmem if needed) that does not need to rewrite a lot of early boot code and can pretty much guarantee success even if memory is tight and fragmented. Hongyan
next prev parent reply other threads:[~2021-05-07 15:00 UTC|newest] Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-05-06 10:42 [PATCH RFC 0/2] Add a design document for Live Updating Xen Julien Grall 2021-05-06 10:42 ` [PATCH RFC 1/2] docs/design: Add a design document for Live Update Julien Grall 2021-05-06 14:43 ` Paul Durrant 2021-05-07 9:18 ` Hongyan Xia 2021-05-07 10:00 ` Julien Grall 2021-05-07 9:52 ` Jan Beulich 2021-05-07 11:44 ` Julien Grall 2021-05-07 12:15 ` Jan Beulich 2021-05-07 14:59 ` Xia, Hongyan [this message] 2021-05-07 15:28 ` Jan Beulich 2021-05-06 10:42 ` [PATCH RFC 2/2] xen/kexec: Reserve KEXEC_TYPE_LIVEUPDATE and KEXEC_RANGE_MA_LIVEUPDATE Julien Grall 2021-05-07 7:59 ` Paul Durrant 2021-05-07 8:24 ` Hongyan Xia 2021-05-07 8:30 ` Jan Beulich
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