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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: |
Fri, 26 Jan 2018 19:46:00 +0000 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
* Peter Maydell (address@hidden) wrote:
> On 26 January 2018 at 15:47, Wei Huang <address@hidden> wrote:
> >
> >
> > On 01/25/2018 02:05 PM, Dr. David Alan Gilbert wrote:
> >> * Wei Huang (address@hidden) wrote:
> >>> innerloop:
> >>> /* clean cache because el2 might still cache guest data under KVM
> >>> */
> >>> dc civac, x2
> >>
> >> Can you explain a bit more about that please; if it's guest
> >> visible acorss migration, doesn't that suggest we need the cache clear
> >> in KVM or QEMU?
> >
> > I think this is ARM specific. This is caused by the inconsistency
> > between guest VM's data accesses and userspace's accesses (in
> > check_guest_ram) at the destination:
> >
> > 1) Because uncacheable (guest) + cacheable (host) ==> uncacheable. So
> > the data accesses from guest VM go directly into memory.
> > 2) QEMU user space will use the cacheable version. So it is possible
> > that data can come from cache, instead of RAM. The difference between
> > (1) and (2) obviously can cause check_guest_ram() to fail sometimes.
>
> 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?
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 <=
- 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, 2018/01/29
- 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