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Re: [Qemu-devel] [PATCH V1 1/1] tests: Add migration test for aarch64
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH V1 1/1] tests: Add migration test for aarch64 |
Date: |
Mon, 29 Jan 2018 10:19:36 +0000 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
* Peter Maydell (address@hidden) wrote:
> On 29 January 2018 at 09:53, Dr. David Alan Gilbert <address@hidden> wrote:
> > * Peter Maydell (address@hidden) wrote:
> >> On 26 January 2018 at 19:46, Dr. David Alan Gilbert <address@hidden> wrote:
> >> > * Peter Maydell (address@hidden) wrote:
> >> >> I think the correct fix here is that your test code should turn
> >> >> its MMU on. Trying to treat guest RAM as uncacheable doesn't work
> >> >> for Arm KVM guests (for the same reason that VGA device video memory
> >> >> doesn't work). If it's RAM your guest has to arrange to map it as
> >> >> Normal Cacheable, and then everything should work fine.
> >> >
> >> > Does this cause problems with migrating at just the wrong point during
> >> > a VM boot?
> >>
> >> It wouldn't surprise me if it did, but I don't think I've ever
> >> tried to provoke that problem...
> >
> > If you think it'll get the RAM contents wrong, it might be best to fail
> > the migration if you can detect the cache is disabled in the guest.
>
> I guess QEMU could look at the value of the "MMU disabled/enabled" bit
> in the guest's system registers, and refuse migration if it's off...
>
> (cc'd Marc, Christoffer to check that I don't have the wrong end
> of the stick about how thin the ice is in the period before the
> guest turns on its MMU...)
OK; I mean it's not nice either way - but a failed migration is better
than one with corrupt RAM.
It's not pretty for cloud users; they do host-evacuations and the like
fully automatically without any knowledge of the state of a VM and hope
for migrations to work in any state.
Dave
> thanks
> -- PMM
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
- [Qemu-devel] [PATCH V1 1/1] tests: Add migration test for aarch64, Wei Huang, 2018/01/24
- Re: [Qemu-devel] [PATCH V1 1/1] tests: Add migration test for aarch64, Dr. David Alan Gilbert, 2018/01/25
- Re: [Qemu-devel] [PATCH V1 1/1] tests: Add migration test for aarch64, Wei Huang, 2018/01/26
- Re: [Qemu-devel] [PATCH V1 1/1] tests: Add migration test for aarch64, Peter Maydell, 2018/01/26
- Re: [Qemu-devel] [PATCH V1 1/1] tests: Add migration test for aarch64, Wei Huang, 2018/01/26
- Re: [Qemu-devel] [PATCH V1 1/1] tests: Add migration test for aarch64, Dr. David Alan Gilbert, 2018/01/26
- Re: [Qemu-devel] [PATCH V1 1/1] tests: Add migration test for aarch64, Peter Maydell, 2018/01/28
- Re: [Qemu-devel] [PATCH V1 1/1] tests: Add migration test for aarch64, Dr. David Alan Gilbert, 2018/01/29
- Re: [Qemu-devel] [PATCH V1 1/1] tests: Add migration test for aarch64, Peter Maydell, 2018/01/29
- Re: [Qemu-devel] [PATCH V1 1/1] tests: Add migration test for aarch64,
Dr. David Alan Gilbert <=
- Re: [Qemu-devel] [PATCH V1 1/1] tests: Add migration test for aarch64, Marc Zyngier, 2018/01/29
- Re: [Qemu-devel] [PATCH V1 1/1] tests: Add migration test for aarch64, Christoffer Dall, 2018/01/31
- Re: [Qemu-devel] [PATCH V1 1/1] tests: Add migration test for aarch64, Ard Biesheuvel, 2018/01/31
- Re: [Qemu-devel] [PATCH V1 1/1] tests: Add migration test for aarch64, Dr. David Alan Gilbert, 2018/01/31
- Re: [Qemu-devel] [PATCH V1 1/1] tests: Add migration test for aarch64, Christoffer Dall, 2018/01/31
- Re: [Qemu-devel] [PATCH V1 1/1] tests: Add migration test for aarch64, Ard Biesheuvel, 2018/01/31
- Re: [Qemu-devel] [PATCH V1 1/1] tests: Add migration test for aarch64, Christoffer Dall, 2018/01/31
- Re: [Qemu-devel] [PATCH V1 1/1] tests: Add migration test for aarch64, Ard Biesheuvel, 2018/01/31
- Re: [Qemu-devel] [PATCH V1 1/1] tests: Add migration test for aarch64, Christoffer Dall, 2018/01/31
- Re: [Qemu-devel] [PATCH V1 1/1] tests: Add migration test for aarch64, Ard Biesheuvel, 2018/01/31