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Re: [Qemu-devel] VFIO use of HOST_PAGE_ALIGN

From: Alex Williamson
Subject: Re: [Qemu-devel] VFIO use of HOST_PAGE_ALIGN
Date: Tue, 26 May 2015 09:22:34 -0600

[cc +alexey]

On Mon, 2015-05-25 at 00:48 -0700, Peter Crosthwaite wrote:
> Hi Alex and all,
> I am working on a patch series to enable multiple CPU architectures to
> run at once. It's a long story, but I have hit a snag in hw/vfio/pci.c
> which AFAICS is the only in-tree system-mode use of HOST_PAGE_ALIGN
> (all usermode code is a non-issue as not looking to support user-mode
> multi-arch yet).
> The problem I face, is that this macro depends on translate-all.c's
> qemu_host_page_size which in turn, depends on TARGET_PAGE_SIZE. I'm
> hoping that one day, TARGET_PAGE_SIZE will be a variable and the users
> of it will know to get the correct value depending on their CPU
> specific code location. vfio is the only one I can't handle. My
> knowledge on vfio is near-0, but my thinking is, since this is not
> arch specific code can we instead use the raw host page alignment
> rather that the CPU arch specific one?

I think we could replace our use of HOST_PAGE_ALIGN with something based
only on the host's getpagesize().  I don't see that we really care about
the target page size for this usage.  Alexey, I think you're the only
arch where host and target page sizes can actually be different, do you
agree?  Thanks,


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