From: Paolo Bonzini <pbonzini@redhat.com>
To: David Hildenbrand <david@redhat.com>, qemu-devel@nongnu.org
Cc: Eduardo Habkost <ehabkost@redhat.com>,
kvm@vger.kernel.org,
"Dr . David Alan Gilbert" <dgilbert@redhat.com>,
Peter Xu <peterx@redhat.com>, Igor Mammedov <imammedo@redhat.com>,
Richard Henderson <rth@twiddle.net>
Subject: Re: [PATCH RFC 4/4] kvm: Implement atomic memory region resizes via region_resize()
Date: Fri, 6 Mar 2020 15:39:39 +0100 [thread overview]
Message-ID: <2b1d9549-5564-94e6-a55f-ca80996c6ef9@redhat.com> (raw)
In-Reply-To: <d5704319-e9b8-be6b-6c95-d2e2edc6614c@redhat.com>
On 06/03/20 15:30, David Hildenbrand wrote:
>> Assuming we're only talking about CPU ioctls (seems like a good
>> approximation) maybe you could use start_exclusive/end_exclusive? The
>> current_cpu->in_exclusive_context assignments can be made conditional on
>> "if (current_cpu)".
>>
>> However that means you have to drop the BQL, see
>> process_queued_cpu_work. It may be a problem.
>>
> Yeah, start_exclusive() is expected to be called without the BQL,
> otherwise the other CPUs would not be able to make progress and can
> eventually be "caught".
>
> It's essentially the same reason why I can't use high-level
> pause_all_vcpus()/resume_all_vcpus(). Will drop the BQL which is very
> bad for resizing code.
But any other synchronization primitive that you do which blocks all
vCPUs will have the same issue, otherwise you get a deadlock.
Paolo
next prev parent reply other threads:[~2020-03-06 14:40 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-03 14:19 [PATCH RFC 0/4] kvm: Implement atomic memory region resizes David Hildenbrand
2020-03-03 14:19 ` [PATCH RFC 1/4] openpic_kvm: Use kvm_device_ioctl() instead of ioctl() David Hildenbrand
2020-03-03 14:19 ` [PATCH RFC 2/4] intc/s390_flic_kvm.c: " David Hildenbrand
2020-03-04 8:22 ` Christian Borntraeger
2020-03-04 8:30 ` David Hildenbrand
2020-03-03 14:19 ` [PATCH RFC 3/4] memory: Add region_resize() callback to memory notifier David Hildenbrand
2020-03-03 14:19 ` [PATCH RFC 4/4] kvm: Implement atomic memory region resizes via region_resize() David Hildenbrand
2020-03-06 9:50 ` Paolo Bonzini
2020-03-06 10:20 ` David Hildenbrand
2020-03-06 11:38 ` Paolo Bonzini
2020-03-06 12:18 ` David Hildenbrand
2020-03-06 14:30 ` David Hildenbrand
2020-03-06 14:39 ` Paolo Bonzini [this message]
2020-03-06 14:44 ` David Hildenbrand
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