Re: 2.6.25-rc1 xen pvops regression

H. Peter Anvin
2008-02-21T22:43:28Z

Ian Campbell wrote:
> On Thu, 2008-02-21 at 13:37 -0800, Jeremy Fitzhardinge wrote:
>> H. Peter Anvin wrote:
>>>> Still curious about why a pagetable page is ending up in that range
>>>> though. Seems like it shouldn't be possible, since we shouldn't be
>>>> allowed to allocate from those pages, at least until the DMI probe
>>>> has happened... Unless the early allocator is only excluded from
>>>> e820 reserved pages, which would cause a problem on systems which
>>>> don't reserve the DMI space... HPA?
>>>>
>>> I thought the problem was a Xen-provided pagetable from before Linux
>>> started?
>> Hm, I don't think so. The domain-builder pagetable is put after the
>> kernel, so it shouldn't be under 1M.
>
> I can confirm that it is Linux which is allocating it. The call path:
> # xm create -c debian-x86_32p-1
> Using config file "/etc/xen/debian-x86_32p-1".
> Started domain debian-1
> xen_alloc_pt_init PFN f0
> Pid: 0, comm: swapper Not tainted 2.6.25-rc2 #68
> [<c02ecb6b>] xen_alloc_pt_init+0x4b/0x60
> [<c02f5e2b>] one_page_table_init+0x8b/0xf0
> [<c02f63df>] paging_init+0x3bf/0x520
> [<c02ee444>] setup_arch+0x2a4/0x410
> [<c02e9a64>] start_kernel+0x64/0x380
> [<c02efd7f>] cpu_detect+0x6f/0xf0
> [<c02ed1a1>] xen_start_kernel+0x2f1/0x310
> =======================
> Entering add_active_range(0, 0, 262144) 0 entries of 256 used
> Zone PFN ranges:
> DMA 0 -> 4096
>

What is the e820 information you feed the kernel? We should only ever
allocate page tables out of available RAM, not any other type of memory
(reserved or not).

-hpa