From 93de2a6a4b91b72607136dd656edf03fb399d27f Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 23 Sep 2026 09:37:21 -0700 Subject: KVM: SEV: Do cache maintenance on the source VM during intra-host migration Manually perform cache maintenance on the source VM during intra-host migration to ensure no stale data is left in CPU caches after the VM is destroyed. Because the source VM is "converted" to a non-SEV VM, KVM's memory reclaim flows won't trigger cache maintenance, e.g. when all guest memory is reclaimed in response to detaching from the mmu_notifier. Note, relying on the destination VM to do cache maintenance isn't an option as KVM doesn't require identical guest memory configurations, i.e. the source VM may have access to memory that the destination VM does not. Enforcing equivalent memory configurations is infeasible, as it would require a *deep* comparison of memslots, e.g. to verify that not only are the memslot identical, but what the memslots point at is also identical. Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration") Cc: stable@vger.kernel.org Reported-by: Stefan Teodorescu Signed-off-by: Sean Christopherson Message-ID: <20260923163721.1584779-3-seanjc@google.com> Signed-off-by: Paolo Bonzini --- Documentation/ABI/testing/sysfs-class-bdi | 134 ++++++++++++++++++++++++++++++ 1 file changed, 134 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-class-bdi (limited to 'Documentation/ABI/testing/sysfs-class-bdi') diff --git a/Documentation/ABI/testing/sysfs-class-bdi b/Documentation/ABI/testing/sysfs-class-bdi new file mode 100644 index 000000000..0d2abd88a --- /dev/null +++ b/Documentation/ABI/testing/sysfs-class-bdi @@ -0,0 +1,134 @@ +What: /sys/class/bdi// +Date: January 2008 +Contact: Peter Zijlstra +Description: + +Provide a place in sysfs for the backing_dev_info object. This allows +setting and retrieving various BDI specific variables. + +The identifier can be either of the following: + +MAJOR:MINOR + + Device number for block devices, or value of st_dev on + non-block filesystems which provide their own BDI, such as NFS + and FUSE. + +MAJOR:MINOR-fuseblk + + Value of st_dev on fuseblk filesystems. + +default + + The default backing dev, used for non-block device backed + filesystems which do not provide their own BDI. + +What: /sys/class/bdi//read_ahead_kb +Date: January 2008 +Contact: Peter Zijlstra +Description: + Size of the read-ahead window in kilobytes + + (read-write) +What: /sys/class/bdi//min_ratio +Date: January 2008 +Contact: Peter Zijlstra +Description: + Under normal circumstances each device is given a part of the + total write-back cache that relates to its current average + writeout speed in relation to the other devices. + + The 'min_ratio' parameter allows assigning a minimum + percentage of the write-back cache to a particular device. + For example, this is useful for providing a minimum QoS. + + (read-write) + +What: /sys/class/bdi//min_ratio_fine +Date: November 2022 +Contact: Stefan Roesch +Description: + Under normal circumstances each device is given a part of the + total write-back cache that relates to its current average + writeout speed in relation to the other devices. + + The 'min_ratio_fine' parameter allows assigning a minimum reserve + of the write-back cache to a particular device. The value is + expressed as part of 1 million. For example, this is useful for + providing a minimum QoS. + + (read-write) + +What: /sys/class/bdi//max_ratio +Date: January 2008 +Contact: Peter Zijlstra +Description: + Allows limiting a particular device to use not more than the + given percentage of the write-back cache. This is useful in + situations where we want to avoid one device taking all or + most of the write-back cache. For example in case of an NFS + mount that is prone to get stuck, or a FUSE mount which cannot + be trusted to play fair. + + (read-write) + +What: /sys/class/bdi//max_ratio_fine +Date: November 2022 +Contact: Stefan Roesch +Description: + Allows limiting a particular device to use not more than the + given value of the write-back cache. The value is given as part + of 1 million. This is useful in situations where we want to avoid + one device taking all or most of the write-back cache. For example + in case of an NFS mount that is prone to get stuck, or a FUSE mount + which cannot be trusted to play fair. + + (read-write) + +What: /sys/class/bdi//min_bytes +Date: October 2022 +Contact: Stefan Roesch +Description: + Under normal circumstances each device is given a part of the + total write-back cache that relates to its current average + writeout speed in relation to the other devices. + + The 'min_bytes' parameter allows assigning a minimum + percentage of the write-back cache to a particular device + expressed in bytes. + For example, this is useful for providing a minimum QoS. + + (read-write) + +What: /sys/class/bdi//max_bytes +Date: October 2022 +Contact: Stefan Roesch +Description: + Allows limiting a particular device to use not more than the + given 'max_bytes' of the write-back cache. This is useful in + situations where we want to avoid one device taking all or + most of the write-back cache. For example in case of an NFS + mount that is prone to get stuck, a FUSE mount which cannot be + trusted to play fair, or a nbd device. + + (read-write) + +What: /sys/class/bdi//strict_limit +Date: October 2022 +Contact: Stefan Roesch +Description: + Forces per-BDI checks for the share of given device in the write-back + cache even before the global background dirty limit is reached. This + is useful in situations where the global limit is much higher than + affordable for given relatively slow (or untrusted) device. Turning + strictlimit on has no visible effect if max_ratio is equal to 100%. + + (read-write) +What: /sys/class/bdi//stable_pages_required +Date: January 2008 +Contact: Peter Zijlstra +Description: + If set, the backing device requires that all pages comprising a write + request must not be changed until writeout is complete. + + (read-only) -- cgit v1.3.1