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Re: [PATCH v3 2/2] vhost: Only align sections for vhost-user
From: |
Michael S. Tsirkin |
Subject: |
Re: [PATCH v3 2/2] vhost: Only align sections for vhost-user |
Date: |
Fri, 17 Jan 2020 09:25:34 -0500 |
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.
>
> Paolo
So right now remote will query the fd passed to get the alignment.
You are basically saying it's not enough in some cases?
--
MST
[PATCH v3 1/2] vhost: Add names to section rounded warning, Dr. David Alan Gilbert (git), 2020/01/16
Re: [PATCH v3 0/2] Fix hyperv synic on vhost, no-reply, 2020/01/16