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