Messages in this thread | | | Date | Tue, 26 Apr 2011 16:34:36 +0200 | From | Daniel Kiper <> | Subject | Re: [PATCH REPOST] pv-grub: Fix for incorrect dom->p2m_host[] list initialization |
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On Tue, Apr 26, 2011 at 09:42:42AM -0400, Konrad Rzeszutek Wilk wrote: > On Fri, Apr 22, 2011 at 11:25:45PM +0200, Daniel Kiper wrote: > > Added missed Signed-off-by line. > > > > After a lot of debugging and long reading of Linux Kernel and Xen code > > finally I killed deeply hidden bug in pv-grub. Details below. > > Additionally, I am CC'ing this e-mail to LKML because this issue > > looks like Linux Kernel problem, however, it is not. > > > > This patch applies to Xen Ver. 4.0, Xen Ver. 4.1 and unstable tree. > > > > # HG changeset patch > > # User dkiper@net-space.pl > > # Date 1303474763 -7200 > > # Node ID b33bf24be129b7b9cd2248460beb1298088c6af5 > > # Parent dbf2ddf652dc3dd927447e79ef4bc586de55d708 > > Introduction of Linux Kernel git commit ceefccc93932b920a8ec6f35f596db05202a12fe > > (x86: default CONFIG_PHYSICAL_START and CONFIG_PHYSICAL_ALIGN to 16 MB) revealed > > deeply hidden bug in pv-grub. During kernel load stage dom->p2m_host[] list has > > been incorrectly initialized. > > > > At the beginning of kernel load stage dom->p2m_host[] list is populated with > > current pfn->mfn layout. Later during memory allocation (memory is allocated > > page by page in kexec_allocate()) page order is changed to establish linear > > layout in new domain. It is done by exchanging subsequent mfns with newly > > allocated mfns. dom->p2m_host[] list is indexed by currently requested pfn > > (it is incremented from 0) and pfn of newly allocated paged. If pfn of newly > > allocated page is less than currently requested pfn then relevant earlier > > allocated mfn is overwritten which leads to domain crash later. This patch > > fix that issue. If pfn of newly allocated page is less then currently > > requested pfn then relevant pfn/mfn pair is properly calculated and usual > > exchange occurs later. > > Nice! I presume this fixes the issue you had at the Xen Hack-O-Thon with > your guest right?
Yes, it does. It was very difficult to discover because that issue overlapped with other memory management issues which were coming out last time. Currently, I am working on time optimized version of that patch.
Daniel
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