[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [Qemu-devel] [RFC/BUG] xen-mapcache: buggy invalidate map cache?
On Tue, Apr 11, 2017 at 3:50 AM, Stefano Stabellini <sstabellini@xxxxxxxxxx> wrote: > On Mon, 10 Apr 2017, Stefano Stabellini wrote: >> On Mon, 10 Apr 2017, hrg wrote: >> > On Sun, Apr 9, 2017 at 11:55 PM, hrg <hrgstephen@xxxxxxxxx> wrote: >> > > On Sun, Apr 9, 2017 at 11:52 PM, hrg <hrgstephen@xxxxxxxxx> wrote: >> > >> Hi, >> > >> >> > >> In xen_map_cache_unlocked(), map to guest memory maybe in entry->next >> > >> instead of first level entry (if map to rom other than guest memory >> > >> comes first), while in xen_invalidate_map_cache(), when VM ballooned >> > >> out memory, qemu did not invalidate cache entries in linked >> > >> list(entry->next), so when VM balloon back in memory, gfns probably >> > >> mapped to different mfns, thus if guest asks device to DMA to these >> > >> GPA, qemu may DMA to stale MFNs. >> > >> >> > >> So I think in xen_invalidate_map_cache() linked lists should also be >> > >> checked and invalidated. >> > >> >> > >> What’s your opinion? Is this a bug? Is my analyze correct? >> >> Yes, you are right. We need to go through the list for each element of >> the array in xen_invalidate_map_cache. Can you come up with a patch? > > I spoke too soon. In the regular case there should be no locked mappings > when xen_invalidate_map_cache is called (see the DPRINTF warning at the > beginning of the functions). Without locked mappings, there should never > be more than one element in each list (see xen_map_cache_unlocked: > entry->lock == true is a necessary condition to append a new entry to > the list, otherwise it is just remapped). > > Can you confirm that what you are seeing are locked mappings > when xen_invalidate_map_cache is called? To find out, enable the DPRINTK > by turning it into a printf or by defininig MAPCACHE_DEBUG. In fact, I think the DPRINTF above is incorrect too. In pci_add_option_rom(), rtl8139 rom is locked mapped in pci_add_option_rom->memory_region_get_ram_ptr (after memory_region_init_ram). So actually I think we should remove the DPRINTF warning as it is normal. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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