From: David Hildenbrand <david@redhat.com>
To: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>,
"Michael S . Tsirkin" <mst@redhat.com>,
Markus Armbruster <armbru@redhat.com>,
qemu-devel@nongnu.org, Greg Kurz <groug@kaod.org>,
Alex Williamson <alex.williamson@redhat.com>,
Murilo Opsfelder Araujo <muriloo@linux.ibm.com>,
Paolo Bonzini <pbonzini@redhat.com>, Stefan Weil <sw@weilnetz.de>,
Richard Henderson <rth@twiddle.net>
Subject: Re: [PATCH v1 00/13] Ram blocks with resizable anonymous allocations under POSIX
Date: Mon, 10 Feb 2020 10:47:15 +0100 [thread overview]
Message-ID: <b7775909-dba8-fbf7-0334-a0c246bf84df@redhat.com> (raw)
In-Reply-To: <20200207152847.GG3302@work-vm>
>> That should work as expected. Resizing *while* kvm is running is tricky, but that‘s not part of this series and a different story :) right now, resizing is only valid on reboot/incoming migration.
>
> Hmm 'when' during an incoming migration; I ask because of userfaultfd
> setup for postcopy. Also note those things can combine - i.e. a reboot
> that happens during a migration (we've already got a pile of related
> bugs).
Yes, resizing while migration is in progress (source already sent the rem block sizes,
receiving side in postcopy), or when dumping is active is bad. In general,
resizing while *somebody* thinks the used_length of a ram block won't change is bad.
Incoming migration: migration/ram.c: ram_load_precopy(): RAM_SAVE_FLAG_MEM_SIZE
So in preload, before the guest is running and before postcopy has started.
At that point, performing the resize is fine.
>
>>>
>>> c) It's interesting this is keyed off the RAMBlock notifiers - do
>>> memory_listener's on the address space the block is mapped into get
>>> triggered? I'm wondering how vhost (and vhost-user) in particular
>>> see this.
>>
>> Yes, memory listeners get triggered. Old region is removed, new one is added. Nothing changed on that front.
>>
>> The issue with ram block notifiers is that they did not do a „remove old, add new“ on resizes. They only added the full ram block. Bad. E.g., vfio wants to pin all memory - which would fail on PROT_NONE.
>>
>> E.g., for HAX, there is no kernel ioctl to remove a ram block ... for SEV there is, but I am not sure about the implications when converting back and forth between encrypted/unencrypted. So SEV and HAX require legacy handling.
>
> I guess for a memory listener it just sees a new layout after the commit
> and then can figure out what changed.
Exactly.
--
Thanks,
David / dhildenb
prev parent reply other threads:[~2020-02-10 9:48 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-03 18:31 [PATCH v1 00/13] Ram blocks with resizable anonymous allocations under POSIX David Hildenbrand
2020-02-03 18:31 ` [PATCH v1 01/13] util: vfio-helpers: Factor out and fix processing of existings ram blocks David Hildenbrand
2020-02-03 18:31 ` [PATCH v1 02/13] exec: Factor out setting ram settings (madvise ...) into qemu_ram_apply_settings() David Hildenbrand
2020-02-06 11:42 ` Richard Henderson
2020-02-03 18:31 ` [PATCH v1 03/13] exec: Reuse qemu_ram_apply_settings() in qemu_ram_remap() David Hildenbrand
2020-02-06 11:43 ` Richard Henderson
2020-02-03 18:31 ` [PATCH v1 04/13] exec: Drop "shared" parameter from ram_block_add() David Hildenbrand
2020-02-06 11:44 ` Richard Henderson
2020-02-03 18:31 ` [PATCH v1 05/13] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize() David Hildenbrand
2020-02-05 19:37 ` Murilo Opsfelder Araújo
2020-02-06 11:46 ` Richard Henderson
2020-02-03 18:31 ` [PATCH v1 06/13] util/mmap-alloc: Factor out reserving of a memory region to mmap_reserve() David Hildenbrand
2020-02-05 19:40 ` Murilo Opsfelder Araújo
2020-02-06 11:55 ` Richard Henderson
2020-02-06 13:16 ` David Hildenbrand
2020-02-03 18:31 ` [PATCH v1 07/13] util/mmap-alloc: Factor out populating of memory to mmap_populate() David Hildenbrand
2020-02-05 19:56 ` Murilo Opsfelder Araújo
2020-02-06 9:26 ` David Hildenbrand
2020-02-06 11:59 ` Richard Henderson
2020-02-03 18:31 ` [PATCH v1 08/13] util/mmap-alloc: Prepare for resizable mmaps David Hildenbrand
2020-02-05 23:00 ` Murilo Opsfelder Araújo
2020-02-06 8:52 ` David Hildenbrand
2020-02-06 12:31 ` Murilo Opsfelder Araújo
2020-02-06 13:16 ` David Hildenbrand
2020-02-06 15:13 ` David Hildenbrand
2020-02-06 12:02 ` Richard Henderson
2020-02-03 18:31 ` [PATCH v1 09/13] util/mmap-alloc: Implement " David Hildenbrand
2020-02-06 12:08 ` Richard Henderson
2020-02-06 13:22 ` David Hildenbrand
2020-02-06 15:27 ` David Hildenbrand
2020-02-07 0:29 ` Murilo Opsfelder Araújo
2020-02-10 9:39 ` David Hildenbrand
2020-02-03 18:31 ` [PATCH v1 10/13] numa: Introduce ram_block_notify_resized() and ram_block_notifiers_support_resize() David Hildenbrand
2020-02-03 18:31 ` [PATCH v1 11/13] util: vfio-helpers: Implement ram_block_resized() David Hildenbrand
2020-02-10 13:41 ` David Hildenbrand
2020-02-03 18:31 ` [PATCH v1 12/13] util: oslib: Resizable anonymous allocations under POSIX David Hildenbrand
2020-02-03 18:31 ` [PATCH v1 13/13] exec: Ram blocks with resizable " David Hildenbrand
2020-02-10 10:12 ` David Hildenbrand
2020-02-06 9:27 ` [PATCH v1 00/13] " Michael S. Tsirkin
2020-02-06 9:45 ` David Hildenbrand
2020-02-06 20:11 ` Dr. David Alan Gilbert
2020-02-06 20:31 ` David Hildenbrand
2020-02-07 15:28 ` Dr. David Alan Gilbert
2020-02-10 9:47 ` David Hildenbrand [this message]
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