On Fri, Nov 26, 2021 at 09:51:23AM +0100, David Hildenbrand wrote:
On 26.11.21 03:30, Sasha Levin wrote:From: David Hildenbrand <david@xxxxxxxxxx> [ Upstream commit 61082ad6a6e1f999eef7e7e90046486c87933b1e ] The initial virtio-mem spec states that while unplugged memory should not be read, the device still has to allow for reading unplugged memory inside the usable region. The primary motivation for this default handling was to simplify bringup of virtio-mem, because there were corner cases where Linux might have accidentially read unplugged memory inside added Linux memory blocks. In the meantime, we: 1. Removed /dev/kmem in commit bbcd53c96071 ("drivers/char: remove /dev/kmem for good") 2. Disallowed access to virtio-mem device memory via /dev/mem in commit 2128f4e21aa2 ("virtio-mem: disallow mapping virtio-mem memory via /dev/mem") 3. Sanitized access to virtio-mem device memory via /proc/kcore in commit 0daa322b8ff9 ("fs/proc/kcore: don't read offline sections, logically offline pages and hwpoisoned pages") 4. Sanitized access to virtio-mem device memory via /proc/vmcore in commit ce2814622e84 ("virtio-mem: kdump mode to sanitize /proc/vmcore access") "Accidential" access to unplugged memory is no longer possible; we can support the new VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE feature that will be required by some hypervisors implementing virtio-mem in the near future. Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx> Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx> Cc: Jason Wang <jasowang@xxxxxxxxxx> Cc: Marek Kedzierski <mkedzier@xxxxxxxxxx> Cc: Hui Zhu <teawater@xxxxxxxxx> Cc: Sebastien Boeuf <sebastien.boeuf@xxxxxxxxx> Cc: Pankaj Gupta <pankaj.gupta.linux@xxxxxxxxx> Cc: Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- drivers/virtio/virtio_mem.c | 1 + include/uapi/linux/virtio_mem.h | 9 ++++++--- 2 files changed, 7 insertions(+), 3 deletions(-) diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c index bef8ad6bf4661..78dfdc9c98a1c 100644 --- a/drivers/virtio/virtio_mem.c +++ b/drivers/virtio/virtio_mem.c @@ -2758,6 +2758,7 @@ static unsigned int virtio_mem_features[] = { #if defined(CONFIG_NUMA) && defined(CONFIG_ACPI_NUMA) VIRTIO_MEM_F_ACPI_PXM, #endif + VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE, }; static const struct virtio_device_id virtio_mem_id_table[] = { diff --git a/include/uapi/linux/virtio_mem.h b/include/uapi/linux/virtio_mem.h index 70e01c687d5eb..e9122f1d0e0cb 100644 --- a/include/uapi/linux/virtio_mem.h +++ b/include/uapi/linux/virtio_mem.h @@ -68,9 +68,10 @@ * explicitly triggered (VIRTIO_MEM_REQ_UNPLUG). * * There are no guarantees what will happen if unplugged memory is - * read/written. Such memory should, in general, not be touched. E.g., - * even writing might succeed, but the values will simply be discarded at - * random points in time. + * read/written. In general, unplugged memory should not be touched, because + * the resulting action is undefined. There is one exception: without + * VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE, unplugged memory inside the usable + * region can be read, to simplify creation of memory dumps. * * It can happen that the device cannot process a request, because it is * busy. The device driver has to retry later. @@ -87,6 +88,8 @@ /* node_id is an ACPI PXM and is valid */ #define VIRTIO_MEM_F_ACPI_PXM 0 +/* unplugged memory must not be accessed */ +#define VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE 1 /* --- virtio-mem: guest -> host requests --- */As 2. and 4. are part of v5.16-rc1 but not v5.15-stable Nacked-by: David Hildenbrand <david@xxxxxxxxxx>
I'll drop them, thanks! -- Thanks, Sasha
