| Message ID | 20231023111341.219317-1-david@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v1] virtio-mem: fix division by zero in virtio_mem_activate_memslots_to_plug() | expand |
On Mon, Oct 23, 2023 at 01:13:41PM +0200, David Hildenbrand wrote: > When running with "dynamic-memslots=off", we enter > virtio_mem_activate_memslots_to_plug() to return immediately again > because "vmem->dynamic_memslots == false". However, the compiler might > not optimize out calculating start_idx+end_idx, where we divide by > vmem->memslot_size. In such a configuration, the memslot size is 0 and > we'll get a division by zero: > > (qemu) qom-set vmem0 requested-size 3G > (qemu) q35.sh: line 38: 622940 Floating point exception(core dumped) > > The same is true for virtio_mem_deactivate_unplugged_memslots(), however > we never really reach that code without a prior > virtio_mem_activate_memslots_to_plug() call. > > Let's fix it by simply calling these functions only with > "dynamic-memslots=on". > > This was found when using a debug build of QEMU. > > Reprted-by: Mario Casquero <mcasquer@redhat.com> > Fixes: 177f9b1ee464 ("virtio-mem: Expose device memory dynamically via multiple memslots if enabled") > Cc: Michael S. Tsirkin <mst@redhat.com> > Cc: Maciej S. Szmigiero <maciej.szmigiero@oracle.com> > Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> > --- > hw/virtio/virtio-mem.c | 22 ++++++++++++---------- > 1 file changed, 12 insertions(+), 10 deletions(-) > > diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c > index 9dc3c61b5a..be4b0b364f 100644 > --- a/hw/virtio/virtio-mem.c > +++ b/hw/virtio/virtio-mem.c > @@ -525,9 +525,7 @@ static void virtio_mem_activate_memslots_to_plug(VirtIOMEM *vmem, > vmem->memslot_size; > unsigned int idx; > > - if (!vmem->dynamic_memslots) { > - return; > - } > + assert(vmem->dynamic_memslots); > > /* Activate all involved memslots in a single transaction. */ > memory_region_transaction_begin(); > @@ -547,9 +545,7 @@ static void virtio_mem_deactivate_unplugged_memslots(VirtIOMEM *vmem, > vmem->memslot_size; > unsigned int idx; > > - if (!vmem->dynamic_memslots) { > - return; > - } > + assert(vmem->dynamic_memslots); > > /* Deactivate all memslots with unplugged blocks in a single transaction. */ > memory_region_transaction_begin(); > @@ -598,7 +594,9 @@ static int virtio_mem_set_block_state(VirtIOMEM *vmem, uint64_t start_gpa, > virtio_mem_notify_unplug(vmem, offset, size); > virtio_mem_set_range_unplugged(vmem, start_gpa, size); > /* Deactivate completely unplugged memslots after updating the state. */ > - virtio_mem_deactivate_unplugged_memslots(vmem, offset, size); > + if (vmem->dynamic_memslots) { > + virtio_mem_deactivate_unplugged_memslots(vmem, offset, size); > + } > return 0; > } > > @@ -635,9 +633,11 @@ static int virtio_mem_set_block_state(VirtIOMEM *vmem, uint64_t start_gpa, > * blocks we are plugging here. The following notification will inform > * registered listeners about the blocks we're plugging. > */ > - virtio_mem_activate_memslots_to_plug(vmem, offset, size); > + if (vmem->dynamic_memslots) { > + virtio_mem_activate_memslots_to_plug(vmem, offset, size); > + } > ret = virtio_mem_notify_plug(vmem, offset, size); > - if (ret) { > + if (ret && vmem->dynamic_memslots) { > virtio_mem_deactivate_unplugged_memslots(vmem, offset, size); > } > } > @@ -749,7 +749,9 @@ static int virtio_mem_unplug_all(VirtIOMEM *vmem) > notifier_list_notify(&vmem->size_change_notifiers, &vmem->size); > > /* Deactivate all memslots after updating the state. */ > - virtio_mem_deactivate_unplugged_memslots(vmem, 0, region_size); > + if (vmem->dynamic_memslots) { > + virtio_mem_deactivate_unplugged_memslots(vmem, 0, region_size); > + } > } > > trace_virtio_mem_unplugged_all(); > -- > 2.41.0
On 23.10.2023 13:13, David Hildenbrand wrote: > When running with "dynamic-memslots=off", we enter > virtio_mem_activate_memslots_to_plug() to return immediately again > because "vmem->dynamic_memslots == false". However, the compiler might > not optimize out calculating start_idx+end_idx, where we divide by > vmem->memslot_size. In such a configuration, the memslot size is 0 and > we'll get a division by zero: > > (qemu) qom-set vmem0 requested-size 3G > (qemu) q35.sh: line 38: 622940 Floating point exception(core dumped) > > The same is true for virtio_mem_deactivate_unplugged_memslots(), however > we never really reach that code without a prior > virtio_mem_activate_memslots_to_plug() call. > > Let's fix it by simply calling these functions only with > "dynamic-memslots=on". > > This was found when using a debug build of QEMU. > > Reprted-by: Mario Casquero <mcasquer@redhat.com> > Fixes: 177f9b1ee464 ("virtio-mem: Expose device memory dynamically via multiple memslots if enabled") > Cc: Michael S. Tsirkin <mst@redhat.com> > Cc: Maciej S. Szmigiero <maciej.szmigiero@oracle.com> > Signed-off-by: David Hildenbrand <david@redhat.com> > --- Reviewed-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com> Thanks, Maciej
This patch has been successfully tested by QE. With a debug QEMU build, start a VM with a virtio-mem device and 'dynamic-memslots=off', this one can be resized seamlessly, no floating point exception found. Tested-by: Mario Casquero <mcasquer@redhat.com> On Mon, Oct 23, 2023 at 1:13 PM David Hildenbrand <david@redhat.com> wrote: > > When running with "dynamic-memslots=off", we enter > virtio_mem_activate_memslots_to_plug() to return immediately again > because "vmem->dynamic_memslots == false". However, the compiler might > not optimize out calculating start_idx+end_idx, where we divide by > vmem->memslot_size. In such a configuration, the memslot size is 0 and > we'll get a division by zero: > > (qemu) qom-set vmem0 requested-size 3G > (qemu) q35.sh: line 38: 622940 Floating point exception(core dumped) > > The same is true for virtio_mem_deactivate_unplugged_memslots(), however > we never really reach that code without a prior > virtio_mem_activate_memslots_to_plug() call. > > Let's fix it by simply calling these functions only with > "dynamic-memslots=on". > > This was found when using a debug build of QEMU. > > Reprted-by: Mario Casquero <mcasquer@redhat.com> > Fixes: 177f9b1ee464 ("virtio-mem: Expose device memory dynamically via multiple memslots if enabled") > Cc: Michael S. Tsirkin <mst@redhat.com> > Cc: Maciej S. Szmigiero <maciej.szmigiero@oracle.com> > Signed-off-by: David Hildenbrand <david@redhat.com> > --- > hw/virtio/virtio-mem.c | 22 ++++++++++++---------- > 1 file changed, 12 insertions(+), 10 deletions(-) > > diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c > index 9dc3c61b5a..be4b0b364f 100644 > --- a/hw/virtio/virtio-mem.c > +++ b/hw/virtio/virtio-mem.c > @@ -525,9 +525,7 @@ static void virtio_mem_activate_memslots_to_plug(VirtIOMEM *vmem, > vmem->memslot_size; > unsigned int idx; > > - if (!vmem->dynamic_memslots) { > - return; > - } > + assert(vmem->dynamic_memslots); > > /* Activate all involved memslots in a single transaction. */ > memory_region_transaction_begin(); > @@ -547,9 +545,7 @@ static void virtio_mem_deactivate_unplugged_memslots(VirtIOMEM *vmem, > vmem->memslot_size; > unsigned int idx; > > - if (!vmem->dynamic_memslots) { > - return; > - } > + assert(vmem->dynamic_memslots); > > /* Deactivate all memslots with unplugged blocks in a single transaction. */ > memory_region_transaction_begin(); > @@ -598,7 +594,9 @@ static int virtio_mem_set_block_state(VirtIOMEM *vmem, uint64_t start_gpa, > virtio_mem_notify_unplug(vmem, offset, size); > virtio_mem_set_range_unplugged(vmem, start_gpa, size); > /* Deactivate completely unplugged memslots after updating the state. */ > - virtio_mem_deactivate_unplugged_memslots(vmem, offset, size); > + if (vmem->dynamic_memslots) { > + virtio_mem_deactivate_unplugged_memslots(vmem, offset, size); > + } > return 0; > } > > @@ -635,9 +633,11 @@ static int virtio_mem_set_block_state(VirtIOMEM *vmem, uint64_t start_gpa, > * blocks we are plugging here. The following notification will inform > * registered listeners about the blocks we're plugging. > */ > - virtio_mem_activate_memslots_to_plug(vmem, offset, size); > + if (vmem->dynamic_memslots) { > + virtio_mem_activate_memslots_to_plug(vmem, offset, size); > + } > ret = virtio_mem_notify_plug(vmem, offset, size); > - if (ret) { > + if (ret && vmem->dynamic_memslots) { > virtio_mem_deactivate_unplugged_memslots(vmem, offset, size); > } > } > @@ -749,7 +749,9 @@ static int virtio_mem_unplug_all(VirtIOMEM *vmem) > notifier_list_notify(&vmem->size_change_notifiers, &vmem->size); > > /* Deactivate all memslots after updating the state. */ > - virtio_mem_deactivate_unplugged_memslots(vmem, 0, region_size); > + if (vmem->dynamic_memslots) { > + virtio_mem_deactivate_unplugged_memslots(vmem, 0, region_size); > + } > } > > trace_virtio_mem_unplugged_all(); > -- > 2.41.0 >
On 23.10.23 13:13, David Hildenbrand wrote: > When running with "dynamic-memslots=off", we enter > virtio_mem_activate_memslots_to_plug() to return immediately again > because "vmem->dynamic_memslots == false". However, the compiler might > not optimize out calculating start_idx+end_idx, where we divide by > vmem->memslot_size. In such a configuration, the memslot size is 0 and > we'll get a division by zero: > > (qemu) qom-set vmem0 requested-size 3G > (qemu) q35.sh: line 38: 622940 Floating point exception(core dumped) > > The same is true for virtio_mem_deactivate_unplugged_memslots(), however > we never really reach that code without a prior > virtio_mem_activate_memslots_to_plug() call. > > Let's fix it by simply calling these functions only with > "dynamic-memslots=on". > > This was found when using a debug build of QEMU. > > Reprted-by: Mario Casquero <mcasquer@redhat.com> > Fixes: 177f9b1ee464 ("virtio-mem: Expose device memory dynamically via multiple memslots if enabled") > Cc: Michael S. Tsirkin <mst@redhat.com> > Cc: Maciej S. Szmigiero <maciej.szmigiero@oracle.com> > Signed-off-by: David Hildenbrand <david@redhat.com> > --- Queued to https://github.com/davidhildenbrand/qemu.git mem-next
diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c index 9dc3c61b5a..be4b0b364f 100644 --- a/hw/virtio/virtio-mem.c +++ b/hw/virtio/virtio-mem.c @@ -525,9 +525,7 @@ static void virtio_mem_activate_memslots_to_plug(VirtIOMEM *vmem, vmem->memslot_size; unsigned int idx; - if (!vmem->dynamic_memslots) { - return; - } + assert(vmem->dynamic_memslots); /* Activate all involved memslots in a single transaction. */ memory_region_transaction_begin(); @@ -547,9 +545,7 @@ static void virtio_mem_deactivate_unplugged_memslots(VirtIOMEM *vmem, vmem->memslot_size; unsigned int idx; - if (!vmem->dynamic_memslots) { - return; - } + assert(vmem->dynamic_memslots); /* Deactivate all memslots with unplugged blocks in a single transaction. */ memory_region_transaction_begin(); @@ -598,7 +594,9 @@ static int virtio_mem_set_block_state(VirtIOMEM *vmem, uint64_t start_gpa, virtio_mem_notify_unplug(vmem, offset, size); virtio_mem_set_range_unplugged(vmem, start_gpa, size); /* Deactivate completely unplugged memslots after updating the state. */ - virtio_mem_deactivate_unplugged_memslots(vmem, offset, size); + if (vmem->dynamic_memslots) { + virtio_mem_deactivate_unplugged_memslots(vmem, offset, size); + } return 0; } @@ -635,9 +633,11 @@ static int virtio_mem_set_block_state(VirtIOMEM *vmem, uint64_t start_gpa, * blocks we are plugging here. The following notification will inform * registered listeners about the blocks we're plugging. */ - virtio_mem_activate_memslots_to_plug(vmem, offset, size); + if (vmem->dynamic_memslots) { + virtio_mem_activate_memslots_to_plug(vmem, offset, size); + } ret = virtio_mem_notify_plug(vmem, offset, size); - if (ret) { + if (ret && vmem->dynamic_memslots) { virtio_mem_deactivate_unplugged_memslots(vmem, offset, size); } } @@ -749,7 +749,9 @@ static int virtio_mem_unplug_all(VirtIOMEM *vmem) notifier_list_notify(&vmem->size_change_notifiers, &vmem->size); /* Deactivate all memslots after updating the state. */ - virtio_mem_deactivate_unplugged_memslots(vmem, 0, region_size); + if (vmem->dynamic_memslots) { + virtio_mem_deactivate_unplugged_memslots(vmem, 0, region_size); + } } trace_virtio_mem_unplugged_all();
When running with "dynamic-memslots=off", we enter virtio_mem_activate_memslots_to_plug() to return immediately again because "vmem->dynamic_memslots == false". However, the compiler might not optimize out calculating start_idx+end_idx, where we divide by vmem->memslot_size. In such a configuration, the memslot size is 0 and we'll get a division by zero: (qemu) qom-set vmem0 requested-size 3G (qemu) q35.sh: line 38: 622940 Floating point exception(core dumped) The same is true for virtio_mem_deactivate_unplugged_memslots(), however we never really reach that code without a prior virtio_mem_activate_memslots_to_plug() call. Let's fix it by simply calling these functions only with "dynamic-memslots=on". This was found when using a debug build of QEMU. Reprted-by: Mario Casquero <mcasquer@redhat.com> Fixes: 177f9b1ee464 ("virtio-mem: Expose device memory dynamically via multiple memslots if enabled") Cc: Michael S. Tsirkin <mst@redhat.com> Cc: Maciej S. Szmigiero <maciej.szmigiero@oracle.com> Signed-off-by: David Hildenbrand <david@redhat.com> --- hw/virtio/virtio-mem.c | 22 ++++++++++++---------- 1 file changed, 12 insertions(+), 10 deletions(-)