Re: [Xen-devel] [PATCH v3 1/1] Add pci_hole_min_size

[Don Slutz <dslutz@xxxxxxxxxxx>]

On 07/01/14 08:48, Jan Beulich wrote:
> > > > On 01.07.14 at 13:56, <dslutz@xxxxxxxxxxx> wrote:
> > On 06/27/14 04:34, Jan Beulich wrote:
> > > Furthermore the whole concept collides with the auto-growing of
> > > the hole immediately following this code. Both logically (both having
> > > a similar purpose) and, what's worse, functionally in that the
> > > shifting done there requires that ((1ULL << 32) - pci_mem_start)
> > > be a power of 2. An option might be to skip this auto-sizing if the
> > > option was given.
> > I am fine with disabling the auto-growing (since as far as I know
> > this is bug #28 (
> >
> >
> >    #28 - support PCI hole resize in qemu-xen
> >
> > )
> But that's only with upstream qemu I suppose; the auto-resizing
> was added for a reason (see the history of the file). So this is
> definitely not going to be an unconditional disabling (other than
> what I kind of read from your reply).
I was not clear.  I am thinking that if pci_hole_min_size (or what ever
the name is) is non-zero (i.e. not default (could be exists also)), I would
disable the auto-resizing code.  As far as I know, the auto-resizing only
works with qemu-xen-traditional.  I was not planning to add
max-ram-below-4g to qemu-xen-traditional (but it would not be a big
patch nor as complex as what is in qemu-xen (upstream master)).

so currently it would be:

+   }
+    else
+   {
/*
     * At the moment qemu-xen can't deal with relocated memory regions.
     * It's too close to the release to make a proper fix; for now,
     * only allow the MMIO hole to grow large enough to move guest memory
     * if we're running qemu-traditional.  Items that don't fit will be
     * relocated into the 64-bit address space.
*
     * This loop now does the following:
     * - If allow_memory_relocate, increase the MMIO hole until it's
     *   big enough, or until it's 2GiB
     * - If !allow_memory_relocate, increase the MMIO hole until it's
     *   big enough, or until it's 2GiB, or until it overlaps guest
     * memory
     */
    while ( (mmio_total > (pci_mem_end - pci_mem_start))
            && ((pci_mem_start << 1) != 0)
            && (allow_memory_relocate
                || (((pci_mem_start << 1) >> PAGE_SHIFT)
                    >= hvm_info->low_mem_pgend)) )
        pci_mem_start <<= 1;
+  }



But looking closer I could just set:

HVM_XS_ALLOW_MEMORY_RELOCATE to 0

to stop part of this.  And the other part should be false do to
xc_hvm_build_with_hole()

but this will need testing.

     -Don Slutz


> Jan

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