On 2014-02-24 17:30:55 Mon, Laurent Dufour wrote:
> In copy_oldmem_page, the current check using max_pfn and min_low_pfn to
> decide if the page is backed or not, is not valid when the memory layout is
> not continuous.
>
> This happens when running as a QEMU/KVM guest, where RTAS is mapped higher
> in the memory. In that case max_pfn points to the end of RTAS, and a hole
> between the end of the kdump kernel and RTAS is not backed by PTEs. As a
> consequence, the kdump kernel is crashing in copy_oldmem_page when accessing
> in a direct way the pages in that hole.
>
> This fix relies on the memblock's service memblock_is_region_memory to
> check if the read page is part or not of the directly accessible memory.
>
> Signed-off-by: Laurent Dufour <lduf...@linux.vnet.ibm.com>
Tested on PowerNV (BE), where without this patch we see cp and
makedumpfile fails with "Bad address" while reading /proc/vmcore.
With this patch makedumpfile and cp succeeds.
Tested-by: Mahesh Salgaonkar <mah...@linux.vnet.ibm.com>
> ---
> arch/powerpc/kernel/crash_dump.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/kernel/crash_dump.c
> b/arch/powerpc/kernel/crash_dump.c
> index 11c1d06..7a13f37 100644
> --- a/arch/powerpc/kernel/crash_dump.c
> +++ b/arch/powerpc/kernel/crash_dump.c
> @@ -98,17 +98,19 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
> size_t csize, unsigned long offset, int userbuf)
> {
> void *vaddr;
> + phys_addr_t paddr;
>
> if (!csize)
> return 0;
>
> csize = min_t(size_t, csize, PAGE_SIZE);
> + paddr = pfn << PAGE_SHIFT;
>
> - if ((min_low_pfn < pfn) && (pfn < max_pfn)) {
> - vaddr = __va(pfn << PAGE_SHIFT);
> + if (memblock_is_region_memory(paddr, csize)) {
> + vaddr = __va(paddr);
> csize = copy_oldmem_vaddr(vaddr, buf, csize, offset, userbuf);
> } else {
> - vaddr = __ioremap(pfn << PAGE_SHIFT, PAGE_SIZE, 0);
> + vaddr = __ioremap(paddr, PAGE_SIZE, 0);
> csize = copy_oldmem_vaddr(vaddr, buf, csize, offset, userbuf);
> iounmap(vaddr);
> }
>
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--
Mahesh J Salgaonkar
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