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SubjectRe: [PATCH] selftests: kvm/set_memory_region_test: Fix race in move region test
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On 02/12/20 21:35, Maciej S. Szmigiero wrote:
> From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
>
> The current memory region move test correctly handles the situation that
> the second (realigning) memslot move operation would temporarily trigger
> MMIO until it completes, however it does not handle the case in which the
> first (misaligning) move operation does this, too.
> This results in false test assertions in case it does so.
>
> Fix this by handling temporary MMIO from the first memslot move operation
> in the test guest code, too.
>
> Fixes: 8a0639fe9201 ("KVM: sefltests: Add explicit synchronization to move mem region test")
> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> ---
> The race is pretty hard to trigger on the current KVM memslot code,
> to trigger it reliably an extra delay in memslot move op is needed:
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1173,7 +1173,7 @@ static struct kvm_memslots *kvm_dup_memslots(struct kvm_memslots *old,
>
> return slots;
> }
> -
> +#include <linux/delay.h>
> static int kvm_set_memslot(struct kvm *kvm,
> const struct kvm_userspace_memory_region *mem,
> struct kvm_memory_slot *old,
> @@ -1212,6 +1212,8 @@ static int kvm_set_memslot(struct kvm *kvm,
> * - kvm_is_visible_gfn (mmu_check_root)
> */
> kvm_arch_flush_shadow_memslot(kvm, slot);
> +
> + if (change == KVM_MR_MOVE) mdelay(100);
> }
>
> r = kvm_arch_prepare_memory_region(kvm, new, mem, change);
>
> .../selftests/kvm/set_memory_region_test.c | 17 +++++++++++++----
> 1 file changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/set_memory_region_test.c b/tools/testing/selftests/kvm/set_memory_region_test.c
> index b3ece55a2da6..6f441dd9f33c 100644
> --- a/tools/testing/selftests/kvm/set_memory_region_test.c
> +++ b/tools/testing/selftests/kvm/set_memory_region_test.c
> @@ -156,14 +156,23 @@ static void guest_code_move_memory_region(void)
> GUEST_SYNC(0);
>
> /*
> - * Spin until the memory region is moved to a misaligned address. This
> - * may or may not trigger MMIO, as the window where the memslot is
> - * invalid is quite small.
> + * Spin until the memory region starts getting moved to a
> + * misaligned address.
> + * Every region move may or may not trigger MMIO, as the
> + * window where the memslot is invalid is usually quite small.
> */
> val = guest_spin_on_val(0);
> GUEST_ASSERT_1(val == 1 || val == MMIO_VAL, val);
>
> - /* Spin until the memory region is realigned. */
> + /* Spin until the misaligning memory region move completes. */
> + val = guest_spin_on_val(MMIO_VAL);
> + GUEST_ASSERT_1(val == 1 || val == 0, val);
> +
> + /* Spin until the memory region starts to get re-aligned. */
> + val = guest_spin_on_val(0);
> + GUEST_ASSERT_1(val == 1 || val == MMIO_VAL, val);
> +
> + /* Spin until the re-aligning memory region move completes. */
> val = guest_spin_on_val(MMIO_VAL);
> GUEST_ASSERT_1(val == 1, val);
>
>

Queued, thanks.

paolo

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