Re: [Qemu-devel] VFIO use of HOST_PAGE_ALIGN

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 05/27/2015 01:22 AM, Alex Williamson wrote:
> [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?

What is "raw host page" here? I thought qemu_host_page_size is the one, 
where does it depend on TARGET_PAGE_SIZE?


> 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,

Strongly agree. Where it really matters (MSIX), it is already 
qemu_host_page_size and HOST_PAGE_ALIGN and I am a bit scared by that "raw 
host page alignment" :)



-- 
Alexey