[PATCH V2 11/11] mshv: Mark mem regions as non-movable upfront if device passthru

Mukesh R
2026-05-01T00:42:31Z

If a VM is started with device attached, the mem regions must be marked
non-movable as the device attach hypercall right away allows the use of
SLAT for IOMMU. Marking them non-movable forces mapping of the entire
guest RAM in the SLAT at the time of region creation along with the
region pinned. Also, because a device could be dynamically attached
much later in a VM, create a boot parameter to disable movable pages
that users can set if they anticipate such an action.

Signed-off-by: Mukesh R <mrathor@linux.microsoft.com>
---
drivers/hv/mshv_root.h | 1 +
drivers/hv/mshv_root_main.c | 15 ++++++++++++++-
2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/hv/mshv_root.h b/drivers/hv/mshv_root.h
index b9880d0bdc4d..d57c26950203 100644
--- a/drivers/hv/mshv_root.h
+++ b/drivers/hv/mshv_root.h
@@ -141,6 +141,7 @@ struct mshv_partition {
pid_t pt_vmm_tgid;
bool import_completed;
bool pt_initialized;
+ bool pt_regions_pinned;
#if IS_ENABLED(CONFIG_DEBUG_FS)
struct dentry *pt_stats_dentry;
struct dentry *pt_vp_dentry;
diff --git a/drivers/hv/mshv_root_main.c b/drivers/hv/mshv_root_main.c
index a7864463961b..ac71534733bd 100644
--- a/drivers/hv/mshv_root_main.c
+++ b/drivers/hv/mshv_root_main.c
@@ -49,6 +49,10 @@ MODULE_DESCRIPTION("Microsoft Hyper-V root partition VMM interface /dev/mshv");
static bool hv_nofull_mmio; /* don't map entire mmio region upon fault */
module_param(hv_nofull_mmio, bool, 0644);

+static bool hv_no_movbl_pgs; /* disable movable pages completely */
+module_param(hv_no_movbl_pgs, bool, 0644);
+MODULE_PARM_DESC(hv_no_movbl_pgs, "If set, don't do movable pages for VMs");
+
struct mshv_root mshv_root;

enum hv_scheduler_type hv_scheduler_type;
@@ -1303,6 +1307,12 @@ static void mshv_async_hvcall_handler(void *data, u64 *status)
*status = partition->async_hypercall_status;
}

+static bool mshv_do_pt_regions_pinned(struct mshv_partition *pt)
+{
+ return pt->pt_regions_pinned || mshv_partition_encrypted(pt) ||
+ hv_no_movbl_pgs;
+}
+
/*
* NB: caller checks and makes sure mem->size is page aligned
* Returns: 0 with regionpp updated on success, or -errno
@@ -1333,7 +1343,7 @@ static int mshv_partition_create_region(struct mshv_partition *partition,

if (is_mmio)
rg->mreg_type = MSHV_REGION_TYPE_MMIO;
- else if (mshv_partition_encrypted(partition) ||
+ else if (mshv_do_pt_regions_pinned(partition) ||
!mshv_region_movable_init(rg))
rg->mreg_type = MSHV_REGION_TYPE_MEM_PINNED;
else
@@ -1808,6 +1818,9 @@ static long mshv_partition_ioctl_create_device(struct mshv_partition *partition,
if (copy_to_user(uarg, &devargk, sizeof(devargk)))
return -EFAULT; /* cleanup in mshv_device_fop_release() */

+ /* For now, all regions must be pinned if there is device passthru. */
+ partition->pt_regions_pinned = true;
+
return 0;

undo_out:
--
2.51.2.vfs.0.1