From: Paolo Bonzini <pbonzini@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: jasowang@redhat.com, vkuznets@redhat.com,
"Dr. David Alan Gilbert \(git\)" <dgilbert@redhat.com>,
qemu-devel@nongnu.org
Subject: Re: [PATCH v3 2/2] vhost: Only align sections for vhost-user
Date: Fri, 17 Jan 2020 16:06:13 +0100 [thread overview]
Message-ID: <7b94df6a-9d7e-da7d-03b9-0f06b66a7936@redhat.com> (raw)
In-Reply-To: <20200117092147-mutt-send-email-mst@kernel.org>
On 17/01/20 15:25, Michael S. Tsirkin wrote:
> On Fri, Jan 17, 2020 at 02:58:47PM +0100, Paolo Bonzini wrote:
>> On 17/01/20 14:40, Michael S. Tsirkin wrote:
>>> We don't really need v2 just to add a field. Compatibility is maintained
>>> using feature bits. Adding that is a subject for another patch.
>>> But I'm not sure I understand why does remote need to know about alignment.
>>> This patch seems to handle it locally ...
>>
>> Because the remote vhost here will not be able to use the synic regions.
>> If it did, it would have the same overlap problem as vhost-kernel.
>>
>> The alignment is needed because, even if you are mapping only [768k,1M)
>> of a 2M hugepage, you need to mmap [0,2M). You can then discard the
>> rest, but IIUC if you only mmap [768k,1M) then the kernel will fail the
>> mmap.
>
> So right now remote will query the fd passed to get the alignment.
It should, but will it? It's not in the spec and I assume QEMU is doing
this alignment work because some server is not doing it. But indeed we
could use a feature bit to say "don't worry I will be doing the right
thing".
Paolo
> You are basically saying it's not enough in some cases?
>
next prev parent reply other threads:[~2020-01-17 15:07 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-16 20:24 [PATCH v3 0/2] Fix hyperv synic on vhost Dr. David Alan Gilbert (git)
2020-01-16 20:24 ` [PATCH v3 1/2] vhost: Add names to section rounded warning Dr. David Alan Gilbert (git)
2020-01-16 20:24 ` [PATCH v3 2/2] vhost: Only align sections for vhost-user Dr. David Alan Gilbert (git)
2020-01-17 12:52 ` Paolo Bonzini
2020-01-17 13:40 ` Michael S. Tsirkin
2020-01-17 13:58 ` Paolo Bonzini
2020-01-17 14:25 ` Michael S. Tsirkin
2020-01-17 15:06 ` Paolo Bonzini [this message]
2020-01-17 15:10 ` Dr. David Alan Gilbert
2020-01-17 0:24 ` [PATCH v3 0/2] Fix hyperv synic on vhost no-reply
2020-01-17 12:47 ` Dr. David Alan Gilbert
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