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[PATCH V6 4/6] kvm: fix zero length mmio searching

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  [PATCH V6 4/6] kvm: fix zero length mmio searching Jason Wang <jasowang@redhat.com> - 2015-09-15 08:50 +0200
    Re: [PATCH V6 4/6] kvm: fix zero length mmio searching Cornelia Huck <cornelia.huck@de.ibm.com> - 2015-09-15 10:00 +0200

#1224665 — [PATCH V6 4/6] kvm: fix zero length mmio searching

Currently, if we had a zero length mmio eventfd assigned on
KVM_MMIO_BUS. It will never be found by kvm_io_bus_cmp() since it
always compares the kvm_io_range() with the length that guest
wrote. This will cause e.g for vhost, kick will be trapped by qemu
userspace instead of vhost. Fixing this by using zero length if an
iodevice is zero length.

Cc: stable@vger.kernel.org
Cc: Gleb Natapov <gleb@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 virt/kvm/kvm_main.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index eb4c9d2..9af68db 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3157,10 +3157,25 @@ static void kvm_io_bus_destroy(struct kvm_io_bus *bus)
 static inline int kvm_io_bus_cmp(const struct kvm_io_range *r1,
 				 const struct kvm_io_range *r2)
 {
-	if (r1->addr < r2->addr)
+	gpa_t addr1 = r1->addr;
+	gpa_t addr2 = r2->addr;
+
+	if (addr1 < addr2)
 		return -1;
-	if (r1->addr + r1->len > r2->addr + r2->len)
+
+	/* If r2->len == 0, match the exact address.  If r2->len != 0,
+	 * accept any overlapping write.  Any order is acceptable for
+	 * overlapping ranges, because kvm_io_bus_get_first_dev ensures
+	 * we process all of them.
+	 */
+	if (r2->len) {
+		addr1 += r1->len;
+		addr2 += r2->len;
+	}
+
+	if (addr1 > addr2)
 		return 1;
+
 	return 0;
 }
 
-- 
2.1.4

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#1224740

On Tue, 15 Sep 2015 14:41:57 +0800
Jason Wang <jasowang@redhat.com> wrote:

> Currently, if we had a zero length mmio eventfd assigned on
> KVM_MMIO_BUS. It will never be found by kvm_io_bus_cmp() since it
> always compares the kvm_io_range() with the length that guest
> wrote. This will cause e.g for vhost, kick will be trapped by qemu
> userspace instead of vhost. Fixing this by using zero length if an
> iodevice is zero length.
> 
> Cc: stable@vger.kernel.org
> Cc: Gleb Natapov <gleb@kernel.org>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
>  virt/kvm/kvm_main.c | 19 +++++++++++++++++--
>  1 file changed, 17 insertions(+), 2 deletions(-)

Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>

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