Re: [Qemu-devel] Re: [PATCHv2] qemu: target library, use it in msix

["Michael S. Tsirkin" <mst@redhat.com>]

On Sun, Sep 27, 2009 at 06:19:05PM +0300, Blue Swirl wrote:
> On Sun, Sep 27, 2009 at 5:24 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
> > On Sun, Sep 27, 2009 at 04:21:29PM +0200, Michael S. Tsirkin wrote:
> >> On Sun, Sep 27, 2009 at 04:14:49PM +0200, Avi Kivity wrote:
> >> > On 09/27/2009 04:08 PM, Michael S. Tsirkin wrote:
> >> >>
> >> >>
> >> >>>> In practice, the only user is now msix and it does not.  It has 0x1000
> >> >>>> as a constant parameter.  For target_phys_addr_t users if we ever have
> >> >>>> them, we'll just add target_phys_page_align. Generally it's unusual for
> >> >>>> devices to care about size of target physical page.
> >> >>>>
> >> >>>>
> >> >>> I'd fill better with uint64_t, at least that won't truncate.
> >> >>>
> >> >> Doesn't naming it target_page_align32 address this concern?
> >> >>
> >> >
> >> > How can the caller (except in your special case) know if it has a
> >> > quantity that will fit in 32 bits?
> >>
> >> It's actually not unusual for devices to limit addressing to 32 bit, whatever
> >> the bus supports.
> >
> > I would say that devices normally have a specific addressing, and should
> > not be using target specific types at all.  This alignment to target
> > page size is actually an unusual thing.
> 
> Actually, AFAICT MSI-X spec (6.8.2, from the MSI entry in Wikipedia)
> only requires a QWORD alignment. There is some blurb about 4k
> alignment, but I think it only describes how software should use the
> structure.
> If this is the case, we could drop the whole target page
> stuff.

The variable MSIX_PAGE_SIZE actually specifies the size of the space
allocated for MSIX in the memory region.  Spec requires locating MSI-X
tables in a 4K region separate from any other device register, so from
that point of view we could just have had
#define MSIX_PAGE_SIZE 0x1000

The main reason I round the space for MSI-X tables up to cpu page size,
is because I have to call cpu_register_physical_memory on it, which
requires that size is a multiple of target page size.


-- 
MST