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Re: [Qemu-devel] [RFC PATCH 0/4] ARM/ARM64 fixes for live memory snapsho
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [RFC PATCH 0/4] ARM/ARM64 fixes for live memory snapshot based on userfaultfd |
Date: |
Thu, 9 Mar 2017 17:46:43 +0000 |
User-agent: |
Mutt/1.7.1 (2016-10-04) |
* Christian Pinto (address@hidden) wrote:
> This patch series introduces a set of fixes to the previous work proposed by
> Hailiang Zhang to enable in QEMU live memory snapshot based
> on userfaultfd. See discussion here:
> http://www.mail-archive.com/address@hidden/msg393118.html
Thanks for posting this,
> These patches apply on top of:
> https://github.com/coloft/qemu/tree/snapshot-v2
> that is the latest version of Hailiang's work, and rely on the latest work on
> userfaultfd available on Andrea Arcangeli's Linux kernel tree:
> https://git.kernel.org/cgit/linux/kernel/git/andrea/aa.git/log/?h=userfault
>
> The original work was mainly tested on x86 tcg machines and was not working
> ARM/ARM64 tcg.
> The fixes presented in this series enable the live memory snapshot
> to work for ARM64 tcg guests running on top of an ARM64 host.
>
> The main problems encountered were:
> - QEMU uses for ARM a memory page size of 1KB. Even though this size is
> not
> supported by the Linux kernel, is is kept for backward compatibility
> with older ARM CPU MMUs. Initial work was write-unprotecting pages with
> a granularity not always aligned with host page size, causing
> userfaultfd
> to fail.
Yes, Power similarly has a 4kb size for the target page size even though
the host kernel is normally a large page size.
> - The VM execution was resumed right before the status of the migration
> was switched from MIGRATION_STATUS_SETUP to MIGRATION_STATUS_ACTIVE.
> This was causing again the VM to trigger a "Bus error", due to wrong
> status of some memory pages.
> - When unprotecting a memory page the flag
> UFFDIO_WRITEPROTECT_MODE_DONTWAKE was used. This way, after a page is
> copied into snapshot file, the virtual machine execution is not resumed.
>
>
> To test the patches on an ARM64 host, boot an ARM64 tcg machine:
>
> qemu-system-aarch64 -machine virt,accel=tcg -cpu cortex-a57\
> -m 256 -kernel Image \
> -initrd rootfs.cpio.gz \
> -append "earlyprintk rw console=ttyAMA0" \
> -net nic -net user \
> -nographic -serial pty -monitor stdio
>
> start migration from QEMU monitor:
>
> (qemu) migrate file:/root/test_snapshot
>
>
> resume VM form snapshot:
>
> qemu-system-aarch64 -machine virt,accel=tcg -cpu cortex-a57\
> -m 256 -kernel Image \
> -initrd rootfs.cpio.gz \
> -append "earlyprintk rw console=ttyAMA0" \
> -net nic -net user \
> -nographic -serial stdio -monitor pty \
> -incoming file:/root/test_snapshot
Nice, what's your use case and how are you dealing with storage?
Dave
> Christian Pinto (4):
> migration/postcopy-ram: check pagefault flags in userfaultfd thread
> migration/ram: Fix for ARM/ARM64 page size
> migration: snapshot thread
> migration/postcopy-ram: ram_set_pages_wp fix
>
> migration/migration.c | 9 +++++----
> migration/postcopy-ram.c | 25 ++++++++-----------------
> migration/ram.c | 18 ++++++++++++++----
> 3 files changed, 27 insertions(+), 25 deletions(-)
>
> --
> 2.11.0
>
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK