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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] mmap_vmcore: skip non-ram pages reported by hypervisors
On 07/07/14 21:33, Andrew Morton wrote: > On Mon, 7 Jul 2014 17:05:49 +0200 Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> > wrote: > >> we have a special check in read_vmcore() handler to check if the page was >> reported as ram or not by the hypervisor (pfn_is_ram()). However, when >> vmcore is read with mmap() no such check is performed. That can lead to >> unpredictable results, e.g. when running Xen PVHVM guest memcpy() after >> mmap() on /proc/vmcore will hang processing HVMMEM_mmio_dm pages creating >> enormous load in both DomU and Dom0. Does make forward progress though? Or is it ending up in a repeatedly retrying the same instruction? Is it failing on a ballooned page in a RAM region? Or is mapping non-RAM regions as well? >> Fix the issue by mapping each non-ram page to the zero page. Keep direct >> path with remap_oldmem_pfn_range() to avoid looping through all pages on >> bare metal. >> >> The issue can also be solved by overriding remap_oldmem_pfn_range() in >> xen-specific code, as remap_oldmem_pfn_range() was been designed for. >> That, however, would involve non-obvious xen code path for all x86 builds >> with CONFIG_XEN_PVHVM=y and would prevent all other hypervisor-specific >> code on x86 arch from doing the same override. The oldmem_pfn_is_ram() is Xen-specific but this problem (ballooned pages) must be common to KVM. How does KVM handle this? David _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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