Re: [PATCH v3 2/2] vhost: Only align sections for vhost-user

[Michael S. Tsirkin]

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