From: Igor Mammedov <imammedo@redhat.com>
To: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: thuth@redhat.com, david@redhat.com, cohuck@redhat.com,
qemu-devel@nongnu.org, qemu-s390x@nongnu.org,
pbonzini@redhat.com
Subject: Re: [Qemu-devel] [PATCH for-4.2 v3 0/2] s390: stop abusing memory_region_allocate_system_memory()
Date: Mon, 5 Aug 2019 10:54:40 +0200 [thread overview]
Message-ID: <20190805105440.33c4dc8a@redhat.com> (raw)
In-Reply-To: <eb897214-2625-1a44-2709-e33560256480@de.ibm.com>
On Fri, 2 Aug 2019 17:04:21 +0200
Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> On 02.08.19 16:59, Christian Borntraeger wrote:
> >
> >
> > On 02.08.19 16:42, Christian Borntraeger wrote:
> >> On 02.08.19 15:32, Igor Mammedov wrote:
> >>> Changelog:
> >>> since v2:
> >>> - break migration from old QEMU (since 2.12-4.1) for guest with >8TB RAM
> >>> and drop migratable aliases patch as was agreed during v2 review
> >>> - drop 4.2 machines patch as it's not prerequisite anymore
> >>> since v1:
> >>> - include 4.2 machines patch for adding compat RAM layout on top
> >>> - 2/4 add missing in v1 patch for splitting too big MemorySection on
> >>> several memslots
> >>> - 3/4 amend code path on alias destruction to ensure that RAMBlock is
> >>> cleaned properly
> >>> - 4/4 add compat machine code to keep old layout (migration-wise) for
> >>> 4.1 and older machines
> >>>
> >>>
> >>> While looking into unifying guest RAM allocation to use hostmem backends
> >>> for initial RAM (especially when -mempath is used) and retiring
> >>> memory_region_allocate_system_memory() API, leaving only single hostmem backend,
> >>> I was inspecting how currently it is used by boards and it turns out several
> >>> boards abuse it by calling the function several times (despite documented contract
> >>> forbiding it).
> >>>
> >>> s390 is one of such boards where KVM limitation on memslot size got propagated
> >>> to board design and memory_region_allocate_system_memory() was abused to satisfy
> >>> KVM requirement for max RAM chunk where memory region alias would suffice.
> >>>
> >>> Unfortunately, memory_region_allocate_system_memory() usage created migration
> >>> dependency where guest RAM is transferred in migration stream as several RAMBlocks
> >>> if it's more than KVM_SLOT_MAX_BYTES. During v2 review it was agreed to ignore
> >>> migration breakage (documenting it in release notes) and leaving only KVM fix.
> >>>
> >>> In order to replace these several RAM chunks with a single memdev and keep it
> >>> working with KVM memslot size limit, following was done:
> >>> * [1/2] split too big RAM chunk inside of KVM code on several memory slots
> >>> if necessary
> >>> * [2/2] drop manual ram splitting in s390 code
> >>>
> >>>
> >>> CC: pbonzini@redhat.com
> >>> CC: qemu-s390x@nongnu.org
> >>> CC: borntraeger@de.ibm.com
> >>> CC: thuth@redhat.com
> >>> CC: david@redhat.com
> >>> CC: cohuck@redhat.com
> >>
> >> With the fixup this patch set seems to work on s390. I can start 9TB guests and
> >> I can migrate smaller guests between 4.1+patch and 4.0 and 3.1. I currently can
> >> not test migration for the 9TB guest due to lack of a 2nd system.
> >
> > I have to correct myself. The 9TB guest started up but it does not seem to do
> > anything useful (it hangs).
>
> Seems that the userspace addr is wrong (its the same).
> [pid 258234] ioctl(10, KVM_SET_USER_MEMORY_REGION, {slot=0, flags=0, guest_phys_addr=0, memory_size=8796091973632, userspace_addr=0x3fff7d00000}) = 0
> [pid 258234] ioctl(10, KVM_SET_USER_MEMORY_REGION, {slot=1, flags=0, guest_phys_addr=0x7fffff00000, memory_size=1099512676352, userspace_addr=0x3fff7d00000}) = 0
It's a bug in 1/2, I forgot to advance mem->ram along with mem->start_addr.
Let me fix it and simulate it on small s390 host (/me sorry for messy patches)
it won't test migration properly but should be sufficient for testing KVM code patch.
next prev parent reply other threads:[~2019-08-05 8:55 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-02 13:32 [Qemu-devel] [PATCH for-4.2 v3 0/2] s390: stop abusing memory_region_allocate_system_memory() Igor Mammedov
2019-08-02 13:32 ` [Qemu-devel] [PATCH for-4.2 v3 1/2] kvm: s390: split too big memory section on several memslots Igor Mammedov
2019-08-02 13:50 ` Christian Borntraeger
2019-08-02 13:32 ` [Qemu-devel] [PATCH for-4.2 v3 2/2] s390: do not call memory_region_allocate_system_memory() multiple times Igor Mammedov
2019-08-02 13:36 ` David Hildenbrand
2019-08-02 13:41 ` Christian Borntraeger
2019-08-02 13:45 ` David Hildenbrand
2019-08-02 14:11 ` [Qemu-devel] [PATCH for-4.2 v3 0/2] s390: stop abusing memory_region_allocate_system_memory() no-reply
2019-08-02 14:42 ` Christian Borntraeger
2019-08-02 14:59 ` Christian Borntraeger
2019-08-02 15:04 ` Christian Borntraeger
2019-08-05 8:54 ` Igor Mammedov [this message]
2019-08-05 15:18 ` Cornelia Huck
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