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SubjectRe: [PATCH] KVM: Fix assigned device MSI-X entry setting leak
On 2012-01-30 19:06, Alex Williamson wrote:
> We need to prioritize our matching when setting MSI-X vector
> entries. Unused entries should only be used if we don't find
> an exact match or else we risk duplicating entries. This was
> causing an ENOSPC return when trying to mask and unmask MSI-X
> vectors based on guest MSI-X table updates.
>
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
>
> ---
>
> The faulting sequence went something like:
>
> Start:
> [0] entry 0, vector A
> [1] entry 1, vector B
> [2] entry 2, vector C
>
> Set entry 1 to 0:
> [0] entry 0, vector A
> [1] entry 1->1, vector B->0
> [2] entry 2, vector C
>
> Set entry 2 to 0:
> [0] entry 0, vector A
> [1] entry 1->2, vector 0->0 <- incorrectly matched
> [2] entry 2, vector C
>
> Set entry 2 to C:
> [0] entry 0, vector A
> [1] entry 2->2, vector 0->C <- incorrectly matched again
> [2] entry 2, vector C
>
> Set entry 1 to B:
> [0] entry 0, vector A
> [1] entry 2, vector C
> [2] entry 2, vector C
> -ENOSPC
>
> Userspace will need to test for this bug (or do we want to set
> a feature flag?).

The latter is much simpler. We did it before.

>
> virt/kvm/assigned-dev.c | 21 +++++++++++++++------
> 1 files changed, 15 insertions(+), 6 deletions(-)
>
> diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
> index 758e3b3..798a090 100644
> --- a/virt/kvm/assigned-dev.c
> +++ b/virt/kvm/assigned-dev.c
> @@ -728,7 +728,7 @@ msix_nr_out:
> static int kvm_vm_ioctl_set_msix_entry(struct kvm *kvm,
> struct kvm_assigned_msix_entry *entry)
> {
> - int r = 0, i;
> + int r = 0, i, unused = -1;
> struct kvm_assigned_dev_kernel *adev;
>
> mutex_lock(&kvm->lock);
> @@ -741,17 +741,26 @@ static int kvm_vm_ioctl_set_msix_entry(struct kvm *kvm,
> goto msix_entry_out;
> }
>
> - for (i = 0; i < adev->entries_nr; i++)
> - if (adev->guest_msix_entries[i].vector == 0 ||
> - adev->guest_msix_entries[i].entry == entry->entry) {
> + for (i = 0; i < adev->entries_nr; i++) {
> + if (unused < 0 && !adev->guest_msix_entries[i].vector)
> + unused = i;
> +
> + if (adev->guest_msix_entries[i].entry == entry->entry) {
> adev->guest_msix_entries[i].entry = entry->entry;
> adev->guest_msix_entries[i].vector = entry->gsi;
> adev->host_msix_entries[i].entry = entry->entry;
> break;
> }
> + }
> +
> if (i == adev->entries_nr) {
> - r = -ENOSPC;
> - goto msix_entry_out;
> + if (unused < 0) {
> + r = -ENOSPC;
> + goto msix_entry_out;
> + }
> + adev->guest_msix_entries[unused].entry = entry->entry;
> + adev->guest_msix_entries[unused].vector = entry->gsi;
> + adev->host_msix_entries[unused].entry = entry->entry;
> }
>
> msix_entry_out:
>

Looks good. Does it fix the masking problems?

Jan

--
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux


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