[PATCH 0/1] virtio: disable partitions scanning for no partitions block

[PATCH 0/1] virtio: disable partitions scanning for no partitions block

[Yury Kamenev]

Some virtio blocks definitely have no partitions and should not be scanned.

Yury Kamenev (1):
  virtio: disable partitions scanning for no partitions block

 drivers/block/virtio_blk.c      | 6 ++++++
 include/uapi/linux/virtio_blk.h | 1 +
 2 files changed, 7 insertions(+)

-- 
2.24.3 (Apple Git-128)

[PATCH 1/1] virtio: disable partitions scanning for no partitions block

[Yury Kamenev]

Signed-off-by: Yury Kamenev <damtev@yandex-team.ru>
---
 drivers/block/virtio_blk.c      | 6 ++++++
 include/uapi/linux/virtio_blk.h | 1 +
 2 files changed, 7 insertions(+)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index b9fa3ef5b57c..17edcfee2208 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -799,6 +799,10 @@ static int virtblk_probe(struct virtio_device *vdev)
 	vblk->disk->flags |= GENHD_FL_EXT_DEVT;
 	vblk->index = index;
 
+	/*Disable partitions scanning for no-partitions block*/
+	if (virtio_has_feature(vdev, VIRTIO_BLK_F_NO_PS))
+		vblk->disk->flags |= GENHD_FL_NO_PART_SCAN;
+
 	/* configure queue flush support */
 	virtblk_update_cache_mode(vdev);
 
@@ -977,6 +981,7 @@ static unsigned int features_legacy[] = {
 	VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE,
 	VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_TOPOLOGY, VIRTIO_BLK_F_CONFIG_WCE,
 	VIRTIO_BLK_F_MQ, VIRTIO_BLK_F_DISCARD, VIRTIO_BLK_F_WRITE_ZEROES,
+	VIRTIO_BLK_F_NO_PS,
 }
 ;
 static unsigned int features[] = {
@@ -984,6 +989,7 @@ static unsigned int features[] = {
 	VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE,
 	VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_TOPOLOGY, VIRTIO_BLK_F_CONFIG_WCE,
 	VIRTIO_BLK_F_MQ, VIRTIO_BLK_F_DISCARD, VIRTIO_BLK_F_WRITE_ZEROES,
+	VIRTIO_BLK_F_NO_PS,
 };
 
 static struct virtio_driver virtio_blk = {
diff --git a/include/uapi/linux/virtio_blk.h b/include/uapi/linux/virtio_blk.h
index d888f013d9ff..f197d07afb05 100644
--- a/include/uapi/linux/virtio_blk.h
+++ b/include/uapi/linux/virtio_blk.h
@@ -40,6 +40,7 @@
 #define VIRTIO_BLK_F_MQ		12	/* support more than one vq */
 #define VIRTIO_BLK_F_DISCARD	13	/* DISCARD is supported */
 #define VIRTIO_BLK_F_WRITE_ZEROES	14	/* WRITE ZEROES is supported */
+#define VIRTIO_BLK_F_NO_PS      16      /* No partitions */
 
 /* Legacy feature bits */
 #ifndef VIRTIO_BLK_NO_LEGACY
-- 
2.24.3 (Apple Git-128)

Re: [PATCH 1/1] virtio: disable partitions scanning for no partitions block

[Stefan Hajnoczi]

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On Thu, May 20, 2021 at 04:39:08PM +0300, Yury Kamenev wrote:

Hi,
Is there a VIRTIO spec change for the new VIRTIO_BLK_F_NO_PS feature
bit? Please send one:
https://www.oasis-open.org/committees/tc_home.php?wg_abbrev=virtio#feedback

GENHD_FL_NO_PART_SCAN is not used much in other drivers. This makes me
wonder if the same use case is addressed through other means with SCSI,
NVMe, etc devices. Maybe Christoph or Jens can weigh in on whether
adding a bit to disable partition scanning for a virtio-blk fits into
the big picture?

Is your goal to avoid accidentally detecting partitions because it's
confusing when that happens?

VIRTIO is currently undergoing auditing and changes to support untrusted
devices. From that perspective adding a device feature bit to disable
partition scanning does not help protect the guest from an untrusted
disk. The guest cannot trust the device, instead the guest itself would
need to be configured to avoid partition scanning of untrusted devices.

Stefan

> Signed-off-by: Yury Kamenev <damtev@yandex-team.ru>
> ---
>  drivers/block/virtio_blk.c      | 6 ++++++
>  include/uapi/linux/virtio_blk.h | 1 +
>  2 files changed, 7 insertions(+)
> 
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index b9fa3ef5b57c..17edcfee2208 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -799,6 +799,10 @@ static int virtblk_probe(struct virtio_device *vdev)
>  	vblk->disk->flags |= GENHD_FL_EXT_DEVT;
>  	vblk->index = index;
>  
> +	/*Disable partitions scanning for no-partitions block*/

Formatting cleanup and rephrasing:

  /* Disable partition scanning for devices with no partitions */

> +	if (virtio_has_feature(vdev, VIRTIO_BLK_F_NO_PS))

I suggest user a more obvious name:

  VIRTIO_BLK_F_NO_PART_SCAN

> +		vblk->disk->flags |= GENHD_FL_NO_PART_SCAN;
> +
>  	/* configure queue flush support */
>  	virtblk_update_cache_mode(vdev);
>  
> @@ -977,6 +981,7 @@ static unsigned int features_legacy[] = {
>  	VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE,
>  	VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_TOPOLOGY, VIRTIO_BLK_F_CONFIG_WCE,
>  	VIRTIO_BLK_F_MQ, VIRTIO_BLK_F_DISCARD, VIRTIO_BLK_F_WRITE_ZEROES,
> +	VIRTIO_BLK_F_NO_PS,
>  }
>  ;
>  static unsigned int features[] = {
> @@ -984,6 +989,7 @@ static unsigned int features[] = {
>  	VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE,
>  	VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_TOPOLOGY, VIRTIO_BLK_F_CONFIG_WCE,
>  	VIRTIO_BLK_F_MQ, VIRTIO_BLK_F_DISCARD, VIRTIO_BLK_F_WRITE_ZEROES,
> +	VIRTIO_BLK_F_NO_PS,
>  };
>  
>  static struct virtio_driver virtio_blk = {
> diff --git a/include/uapi/linux/virtio_blk.h b/include/uapi/linux/virtio_blk.h
> index d888f013d9ff..f197d07afb05 100644
> --- a/include/uapi/linux/virtio_blk.h
> +++ b/include/uapi/linux/virtio_blk.h
> @@ -40,6 +40,7 @@
>  #define VIRTIO_BLK_F_MQ		12	/* support more than one vq */
>  #define VIRTIO_BLK_F_DISCARD	13	/* DISCARD is supported */
>  #define VIRTIO_BLK_F_WRITE_ZEROES	14	/* WRITE ZEROES is supported */
> +#define VIRTIO_BLK_F_NO_PS      16      /* No partitions */
>  
>  /* Legacy feature bits */
>  #ifndef VIRTIO_BLK_NO_LEGACY
> -- 
> 2.24.3 (Apple Git-128)
> 

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Re: [PATCH 1/1] virtio: disable partitions scanning for no partitions block

[Christoph Hellwig]

On Mon, May 24, 2021 at 03:29:22PM +0100, Stefan Hajnoczi wrote:
> GENHD_FL_NO_PART_SCAN is not used much in other drivers. This makes me
> wonder if the same use case is addressed through other means with SCSI,
> NVMe, etc devices. Maybe Christoph or Jens can weigh in on whether
> adding a bit to disable partition scanning for a virtio-blk fits into
> the big picture?
> 
> Is your goal to avoid accidentally detecting partitions because it's
> confusing when that happens?

I'm really confused what the use case is here.  GENHD_FL_NO_PART_SCAN
has four users:

 - the block core setting it for hidden devices, for which the concept
   of paritions doesn't make sense.  Looking back this should have never
   used GENHD_FL_NO_PART_SCAN, and instead the partition scanning code
   should just check GENHD_FL_HIDDEN as well.
 - mmc uses it for boot partitions and rpmb.  I'm not even sure how
   these can be exposed as block devices as they don't require block
   granularity access IIRC, but if the allow block layer access there
   is no reason to ever set these flags.
 - loop is a bit of a mess.  IIRC the story is that originally the
   loop device did not support partitions, then in 2008 support for
   partitions was added by partitioning the minor number space, and
   then in 2011 support for partitions without that parameter was
   added using a new flag in the loop device creation ioctl that uses
   the extended dev_t space added since.  But even that might be
   something we can handled without that flag without breaking the
   userspace ABI
 - m64card sets it for no good reason at all

In other words: in a perfect would GENHD_FL_NO_PART_SCAN would not
exist, and it certainly should not be added to a new driver, never
mind a protocol.

Re: [PATCH 1/1] virtio: disable partitions scanning for no partitions block

[Ulf Hansson]

On Mon, 24 May 2021 at 16:57, Christoph Hellwig <hch@lst.de> wrote:
>
> On Mon, May 24, 2021 at 03:29:22PM +0100, Stefan Hajnoczi wrote:
> > GENHD_FL_NO_PART_SCAN is not used much in other drivers. This makes me
> > wonder if the same use case is addressed through other means with SCSI,
> > NVMe, etc devices. Maybe Christoph or Jens can weigh in on whether
> > adding a bit to disable partition scanning for a virtio-blk fits into
> > the big picture?
> >
> > Is your goal to avoid accidentally detecting partitions because it's
> > confusing when that happens?
>
> I'm really confused what the use case is here.  GENHD_FL_NO_PART_SCAN
> has four users:
>
>  - the block core setting it for hidden devices, for which the concept
>    of paritions doesn't make sense.  Looking back this should have never
>    used GENHD_FL_NO_PART_SCAN, and instead the partition scanning code
>    should just check GENHD_FL_HIDDEN as well.
>  - mmc uses it for boot partitions and rpmb.  I'm not even sure how
>    these can be exposed as block devices as they don't require block
>    granularity access IIRC, but if the allow block layer access there
>    is no reason to ever set these flags.

For RPMB, we have converted them into char devices, thus
GENHD_FL_NO_PART_SCAN is never set for them. The code needs a cleanup
to clarify this.

When it comes to eMMC boot partitions, those can be read/written to as
any other block device. Although, it's unlikely that they need
partitions as they are usually very small, 512Kb or 2MB in that
ballpark. At least, that was the thinking behind it when we added
GENHD_FL_NO_PART_SCAN for them.

If you want to drop GENHD_FL_NO_PART_SCAN for eMMC boot partitions, I
don't think it will be an issue.

>  - loop is a bit of a mess.  IIRC the story is that originally the
>    loop device did not support partitions, then in 2008 support for
>    partitions was added by partitioning the minor number space, and
>    then in 2011 support for partitions without that parameter was
>    added using a new flag in the loop device creation ioctl that uses
>    the extended dev_t space added since.  But even that might be
>    something we can handled without that flag without breaking the
>    userspace ABI
>  - m64card sets it for no good reason at all
>
> In other words: in a perfect would GENHD_FL_NO_PART_SCAN would not
> exist, and it certainly should not be added to a new driver, never
> mind a protocol.
> _______________________________________________
> Virtualization mailing list
> Virtualization@lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/virtualization

Kind regards
Uffe

Re: [PATCH 1/1] virtio: disable partitions scanning for no partitions block

[Paolo Bonzini]

On 24/05/21 21:34, Юрий Каменев wrote:
> Hi
> 
>     Is your goal to avoid accidentally detecting partitions because it's
>     confusing when that happens?
> 
> The main goal is reducing the kernel start time. It might be use useful 
> in tiny systems that use, for example, squashfs images with certainly no 
> partitions. Disabling partitions scanning for these images can save a 
> few tens of milliseconds which can be a significant acceleration for 
> starting such systems.

Perhaps that could be configured in the image, for example in the kernel 
command line?

Paolo

> 24.05.2021, 17:29, "Stefan Hajnoczi" <stefanha@redhat.com>:
> 
>     On Thu, May 20, 2021 at 04:39:08PM +0300, Yury Kamenev wrote:
> 
>     Hi,
>     Is there a VIRTIO spec change for the new VIRTIO_BLK_F_NO_PS feature
>     bit? Please send one:
>     https://www.oasis-open.org/committees/tc_home.php?wg_abbrev=virtio#feedback
>     <https://www.oasis-open.org/committees/tc_home.php?wg_abbrev=virtio#feedback>
> 
>     GENHD_FL_NO_PART_SCAN is not used much in other drivers. This makes me
>     wonder if the same use case is addressed through other means with SCSI,
>     NVMe, etc devices. Maybe Christoph or Jens can weigh in on whether
>     adding a bit to disable partition scanning for a virtio-blk fits into
>     the big picture?
> 
>     Is your goal to avoid accidentally detecting partitions because it's
>     confusing when that happens?
> 
>     VIRTIO is currently undergoing auditing and changes to support untrusted
>     devices. From that perspective adding a device feature bit to disable
>     partition scanning does not help protect the guest from an untrusted
>     disk. The guest cannot trust the device, instead the guest itself would
>     need to be configured to avoid partition scanning of untrusted devices.
> 
>     Stefan
> 
>           Signed-off-by: Yury Kamenev <damtev@yandex-team.ru
>         <mailto:damtev@yandex-team.ru>>
>           ---
>            drivers/block/virtio_blk.c | 6 ++++++
>            include/uapi/linux/virtio_blk.h | 1 +
>            2 files changed, 7 insertions(+)
> 
>           diff --git a/drivers/block/virtio_blk.c
>         b/drivers/block/virtio_blk.c
>           index b9fa3ef5b57c..17edcfee2208 100644
>           --- a/drivers/block/virtio_blk.c
>           +++ b/drivers/block/virtio_blk.c
>           @@ -799,6 +799,10 @@ static int virtblk_probe(struct
>         virtio_device *vdev)
>                    vblk->disk->flags |= GENHD_FL_EXT_DEVT;
>                    vblk->index = index;
> 
>           + /*Disable partitions scanning for no-partitions block*/
> 
> 
>     Formatting cleanup and rephrasing:
> 
>        /* Disable partition scanning for devices with no partitions */
> 
>           + if (virtio_has_feature(vdev, VIRTIO_BLK_F_NO_PS))
> 
> 
>     I suggest user a more obvious name:
> 
>        VIRTIO_BLK_F_NO_PART_SCAN
> 
>           + vblk->disk->flags |= GENHD_FL_NO_PART_SCAN;
>           +
>                    /* configure queue flush support */
>                    virtblk_update_cache_mode(vdev);
> 
>           @@ -977,6 +981,7 @@ static unsigned int features_legacy[] = {
>                    VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE,
>                    VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_TOPOLOGY,
>         VIRTIO_BLK_F_CONFIG_WCE,
>                    VIRTIO_BLK_F_MQ, VIRTIO_BLK_F_DISCARD,
>         VIRTIO_BLK_F_WRITE_ZEROES,
>           + VIRTIO_BLK_F_NO_PS,
>            }
>            ;
>            static unsigned int features[] = {
>           @@ -984,6 +989,7 @@ static unsigned int features[] = {
>                    VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE,
>                    VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_TOPOLOGY,
>         VIRTIO_BLK_F_CONFIG_WCE,
>                    VIRTIO_BLK_F_MQ, VIRTIO_BLK_F_DISCARD,
>         VIRTIO_BLK_F_WRITE_ZEROES,
>           + VIRTIO_BLK_F_NO_PS,
>            };
> 
>            static struct virtio_driver virtio_blk = {
>           diff --git a/include/uapi/linux/virtio_blk.h
>         b/include/uapi/linux/virtio_blk.h
>           index d888f013d9ff..f197d07afb05 100644
>           --- a/include/uapi/linux/virtio_blk.h
>           +++ b/include/uapi/linux/virtio_blk.h
>           @@ -40,6 +40,7 @@
>            #define VIRTIO_BLK_F_MQ 12 /* support more than one vq */
>            #define VIRTIO_BLK_F_DISCARD 13 /* DISCARD is supported */
>            #define VIRTIO_BLK_F_WRITE_ZEROES 14 /* WRITE ZEROES is
>         supported */
>           +#define VIRTIO_BLK_F_NO_PS 16 /* No partitions */
> 
>            /* Legacy feature bits */
>            #ifndef VIRTIO_BLK_NO_LEGACY
>           --
>           2.24.3 (Apple Git-128)
> 

Re: [PATCH 1/1] virtio: disable partitions scanning for no partitions block

[Iurii Kamenev]

Thanks for your remark. I guess it is possible, I will try to rewrite it 
that way.

24.05.2021 22:41, Paolo Bonzini пишет:
> On 24/05/21 21:34, Юрий Каменев wrote:
>> Hi
>>
>>     Is your goal to avoid accidentally detecting partitions because it's
>>     confusing when that happens?
>>
>> The main goal is reducing the kernel start time. It might be use 
>> useful in tiny systems that use, for example, squashfs images with 
>> certainly no partitions. Disabling partitions scanning for these 
>> images can save a few tens of milliseconds which can be a significant 
>> acceleration for starting such systems.
>
> Perhaps that could be configured in the image, for example in the 
> kernel command line?
>
> Paolo
>
>> 24.05.2021, 17:29, "Stefan Hajnoczi" <stefanha@redhat.com>:
>>
>>     On Thu, May 20, 2021 at 04:39:08PM +0300, Yury Kamenev wrote:
>>
>>     Hi,
>>     Is there a VIRTIO spec change for the new VIRTIO_BLK_F_NO_PS feature
>>     bit? Please send one:
>> https://www.oasis-open.org/committees/tc_home.php?wg_abbrev=virtio#feedback
>> <https://www.oasis-open.org/committees/tc_home.php?wg_abbrev=virtio#feedback>
>>
>>     GENHD_FL_NO_PART_SCAN is not used much in other drivers. This 
>> makes me
>>     wonder if the same use case is addressed through other means with 
>> SCSI,
>>     NVMe, etc devices. Maybe Christoph or Jens can weigh in on whether
>>     adding a bit to disable partition scanning for a virtio-blk fits 
>> into
>>     the big picture?
>>
>>     Is your goal to avoid accidentally detecting partitions because it's
>>     confusing when that happens?
>>
>>     VIRTIO is currently undergoing auditing and changes to support 
>> untrusted
>>     devices. From that perspective adding a device feature bit to 
>> disable
>>     partition scanning does not help protect the guest from an untrusted
>>     disk. The guest cannot trust the device, instead the guest itself 
>> would
>>     need to be configured to avoid partition scanning of untrusted 
>> devices.
>>
>>     Stefan
>>
>>           Signed-off-by: Yury Kamenev <damtev@yandex-team.ru
>>         <mailto:damtev@yandex-team.ru>>
>>           ---
>>            drivers/block/virtio_blk.c | 6 ++++++
>>            include/uapi/linux/virtio_blk.h | 1 +
>>            2 files changed, 7 insertions(+)
>>
>>           diff --git a/drivers/block/virtio_blk.c
>>         b/drivers/block/virtio_blk.c
>>           index b9fa3ef5b57c..17edcfee2208 100644
>>           --- a/drivers/block/virtio_blk.c
>>           +++ b/drivers/block/virtio_blk.c
>>           @@ -799,6 +799,10 @@ static int virtblk_probe(struct
>>         virtio_device *vdev)
>>                    vblk->disk->flags |= GENHD_FL_EXT_DEVT;
>>                    vblk->index = index;
>>
>>           + /*Disable partitions scanning for no-partitions block*/
>>
>>
>>     Formatting cleanup and rephrasing:
>>
>>        /* Disable partition scanning for devices with no partitions */
>>
>>           + if (virtio_has_feature(vdev, VIRTIO_BLK_F_NO_PS))
>>
>>
>>     I suggest user a more obvious name:
>>
>>        VIRTIO_BLK_F_NO_PART_SCAN
>>
>>           + vblk->disk->flags |= GENHD_FL_NO_PART_SCAN;
>>           +
>>                    /* configure queue flush support */
>>                    virtblk_update_cache_mode(vdev);
>>
>>           @@ -977,6 +981,7 @@ static unsigned int features_legacy[] = {
>>                    VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE,
>>                    VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_TOPOLOGY,
>>         VIRTIO_BLK_F_CONFIG_WCE,
>>                    VIRTIO_BLK_F_MQ, VIRTIO_BLK_F_DISCARD,
>>         VIRTIO_BLK_F_WRITE_ZEROES,
>>           + VIRTIO_BLK_F_NO_PS,
>>            }
>>            ;
>>            static unsigned int features[] = {
>>           @@ -984,6 +989,7 @@ static unsigned int features[] = {
>>                    VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE,
>>                    VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_TOPOLOGY,
>>         VIRTIO_BLK_F_CONFIG_WCE,
>>                    VIRTIO_BLK_F_MQ, VIRTIO_BLK_F_DISCARD,
>>         VIRTIO_BLK_F_WRITE_ZEROES,
>>           + VIRTIO_BLK_F_NO_PS,
>>            };
>>
>>            static struct virtio_driver virtio_blk = {
>>           diff --git a/include/uapi/linux/virtio_blk.h
>>         b/include/uapi/linux/virtio_blk.h
>>           index d888f013d9ff..f197d07afb05 100644
>>           --- a/include/uapi/linux/virtio_blk.h
>>           +++ b/include/uapi/linux/virtio_blk.h
>>           @@ -40,6 +40,7 @@
>>            #define VIRTIO_BLK_F_MQ 12 /* support more than one vq */
>>            #define VIRTIO_BLK_F_DISCARD 13 /* DISCARD is supported */
>>            #define VIRTIO_BLK_F_WRITE_ZEROES 14 /* WRITE ZEROES is
>>         supported */
>>           +#define VIRTIO_BLK_F_NO_PS 16 /* No partitions */
>>
>>            /* Legacy feature bits */
>>            #ifndef VIRTIO_BLK_NO_LEGACY
>>           --
>>           2.24.3 (Apple Git-128)
>>
>

[PATCH 0/1] virtio: disable partitions scanning for no partitions block

[Yury Kamenev]

Some virtio blocks definitely have no partitions and should not be scanned.

Yury Kamenev (1):
  virtio: disable partitions scanning for no partitions block

 .../admin-guide/kernel-parameters.txt         |  3 +++
 drivers/block/Kconfig                         |  7 +++++
 drivers/block/virtio_blk.c                    | 26 +++++++++++++++++++
 include/uapi/linux/virtio_blk.h               |  2 ++
 4 files changed, 38 insertions(+)

-- 
2.24.3 (Apple Git-128)