On 06/04/2015 03:53 AM, Peter Crosthwaite wrote:
On Wed, Jun 3, 2015 at 4:16 AM, Alexey Kardashevskiy <a...@ozlabs.ru> wrote:
On 06/01/2015 04:27 AM, Peter Crosthwaite wrote:
On Sun, May 31, 2015 at 6:34 AM, Alexey Kardashevskiy <a...@ozlabs.ru>
wrote:
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?
In translate-all.c:
void page_size_init(void)
{
/* NOTE: we can always suppose that qemu_host_page_size >=
TARGET_PAGE_SIZE */
qemu_real_host_page_size = getpagesize();
if (qemu_host_page_size == 0) {
qemu_host_page_size = qemu_real_host_page_size;
}
if (qemu_host_page_size < TARGET_PAGE_SIZE) {
qemu_host_page_size = TARGET_PAGE_SIZE;
}
qemu_host_page_mask = ~(qemu_host_page_size - 1);
}
It is clamped to be at least as big as a the TARGET_PAGE_SIZE.
Ah, just this one. TARGET_PAGE_SIZE is 4K for PPC64 and the actual page size
can be 4K and 64K so that branch never works for PPC64.
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" :)
So the change would be an alternate macro based on
qemu_real_host_page_size which is what I am calling "raw host page
alignment".
Good, I like it. Cannot it be just a qemu_host_page_size? It is a bit
confusing to have both qemu_host_page_size and qemu_real_host_page_size when
even the first name suggests it is something non-static and sort of real :)
Yes based on this, HOST_PAGE_ALIGN is badly named. It is really
aligning to both host and target. Some rename options:
QEMU_PAGE_ALIGN
HOST_TARGET_PAGE_ALIGN
QEMU_HOST_PAGE_ALIGN
or just unqualified PAGE_ALIGN?
Sorry, I have bad taste so I am not the one to ask :) I'd stick to
HOST_PAGE_ALIGN.
--
Alexey
