From c477581ccc6962651d4d6c702a6c3e2fcc5e4205 Mon Sep 17 00:00:00 2001 From: "Dr. David Alan Gilbert" Date: Thu, 2 Jan 2020 11:56:51 +0000 Subject: [PATCH 2/2] kvm: Reallocate dirty_bmap when we change a slot RH-Author: Dr. David Alan Gilbert Message-id: <20200102115651.140177-1-dgilbert@redhat.com> Patchwork-id: 93256 O-Subject: [RHEL-AV-8.2.0 qemu-kvm PATCH 1/1] kvm: Reallocate dirty_bmap when we change a slot Bugzilla: 1772774 RH-Acked-by: Peter Xu RH-Acked-by: Stefan Hajnoczi RH-Acked-by: Laszlo Ersek From: "Dr. David Alan Gilbert" bz: https://bugzilla.redhat.com/show_bug.cgi?id=1772774 brew: https://brewweb.engineering.redhat.com/brew/taskinfo?taskID=25575691 branch: rhel-av-8.2.0 kvm_set_phys_mem can be called to reallocate a slot by something the guest does (e.g. writing to PAM and other chipset registers). This can happen in the middle of a migration, and if we're unlucky it can now happen between the split 'sync' and 'clear'; the clear asserts if there's no bmap to clear. Recreate the bmap whenever we change the slot, keeping the clear path happy. Typically this is triggered by the guest rebooting during a migrate. Corresponds to: https://bugzilla.redhat.com/show_bug.cgi?id=1772774 https://bugzilla.redhat.com/show_bug.cgi?id=1771032 Signed-off-by: Dr. David Alan Gilbert Reviewed-by: Peter Xu (cherry picked from commit 9b3a31c745b61758aaa5466a3a9fc0526d409188) Signed-off-by: Danilo C. L. de Paula --- accel/kvm/kvm-all.c | 44 +++++++++++++++++++++++++++++--------------- 1 file changed, 29 insertions(+), 15 deletions(-) diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c index dc3ed7f..5007bda 100644 --- a/accel/kvm/kvm-all.c +++ b/accel/kvm/kvm-all.c @@ -518,6 +518,27 @@ static int kvm_get_dirty_pages_log_range(MemoryRegionSection *section, #define ALIGN(x, y) (((x)+(y)-1) & ~((y)-1)) +/* Allocate the dirty bitmap for a slot */ +static void kvm_memslot_init_dirty_bitmap(KVMSlot *mem) +{ + /* + * XXX bad kernel interface alert + * For dirty bitmap, kernel allocates array of size aligned to + * bits-per-long. But for case when the kernel is 64bits and + * the userspace is 32bits, userspace can't align to the same + * bits-per-long, since sizeof(long) is different between kernel + * and user space. This way, userspace will provide buffer which + * may be 4 bytes less than the kernel will use, resulting in + * userspace memory corruption (which is not detectable by valgrind + * too, in most cases). + * So for now, let's align to 64 instead of HOST_LONG_BITS here, in + * a hope that sizeof(long) won't become >8 any time soon. + */ + hwaddr bitmap_size = ALIGN(((mem->memory_size) >> TARGET_PAGE_BITS), + /*HOST_LONG_BITS*/ 64) / 8; + mem->dirty_bmap = g_malloc0(bitmap_size); +} + /** * kvm_physical_sync_dirty_bitmap - Sync dirty bitmap from kernel space * @@ -550,23 +571,9 @@ static int kvm_physical_sync_dirty_bitmap(KVMMemoryListener *kml, goto out; } - /* XXX bad kernel interface alert - * For dirty bitmap, kernel allocates array of size aligned to - * bits-per-long. But for case when the kernel is 64bits and - * the userspace is 32bits, userspace can't align to the same - * bits-per-long, since sizeof(long) is different between kernel - * and user space. This way, userspace will provide buffer which - * may be 4 bytes less than the kernel will use, resulting in - * userspace memory corruption (which is not detectable by valgrind - * too, in most cases). - * So for now, let's align to 64 instead of HOST_LONG_BITS here, in - * a hope that sizeof(long) won't become >8 any time soon. - */ if (!mem->dirty_bmap) { - hwaddr bitmap_size = ALIGN(((mem->memory_size) >> TARGET_PAGE_BITS), - /*HOST_LONG_BITS*/ 64) / 8; /* Allocate on the first log_sync, once and for all */ - mem->dirty_bmap = g_malloc0(bitmap_size); + kvm_memslot_init_dirty_bitmap(mem); } d.dirty_bitmap = mem->dirty_bmap; @@ -1067,6 +1074,13 @@ static void kvm_set_phys_mem(KVMMemoryListener *kml, mem->ram = ram; mem->flags = kvm_mem_flags(mr); + if (mem->flags & KVM_MEM_LOG_DIRTY_PAGES) { + /* + * Reallocate the bmap; it means it doesn't disappear in + * middle of a migrate. + */ + kvm_memslot_init_dirty_bitmap(mem); + } err = kvm_set_user_memory_region(kml, mem, true); if (err) { fprintf(stderr, "%s: error registering slot: %s\n", __func__, -- 1.8.3.1