From cc5d96036e01ac330d24b2f0c336d60f82ab4930 Mon Sep 17 00:00:00 2001 From: Fuad Tabba Date: Fri, 21 Aug 2026 07:44:44 +0100 Subject: KVM: arm64: vgic-its: Skip unreachable devices instead of failing the save vgic_its_save_device_tables() aborts with -EINVAL when a device's entry falls outside the device table, which a guest can arrange on its own: an indirect table lets it clear an L1 entry's valid bit without touching GITS_BASER. That fails a save userspace should be able to issue reliably. Skip the device instead, and point the saved DTE chain past it, as commit ad1e686e2378d ("KVM: arm64: vgic-its: Point saved ITEs at the next valid entry") does for ITEs. compute_next_devid_offset() takes the next device off the list whether or not it was saved, so the predecessor would otherwise point at an entry the save never wrote. Restore follows that offset while it stays inside the table being scanned: within an L2 block, or anywhere in a flat table. Both need userspace to remove a memslot under the table, since dropping an L1 entry takes the whole block with it and scan_its_table() stops at the block boundary. Fixes: 57a9a117154c9 ("KVM: arm64: vgic-its: Device table save/restore") Suggested-by: Marc Zyngier Link: https://lore.kernel.org/all/86bjaz5s6v.wl-maz@kernel.org/ Signed-off-by: Fuad Tabba Reviewed-by: Marc Zyngier Link: https://patch.msgid.link/20260821064445.615838-4-fuad.tabba@linux.dev Signed-off-by: Oliver Upton --- arch/arm64/kvm/vgic/vgic-its.c | 32 +++++++++++++++++++------------- 1 file changed, 19 insertions(+), 13 deletions(-) diff --git a/arch/arm64/kvm/vgic/vgic-its.c b/arch/arm64/kvm/vgic/vgic-its.c index 313bf9e802bf..0904ae850c35 100644 --- a/arch/arm64/kvm/vgic/vgic-its.c +++ b/arch/arm64/kvm/vgic/vgic-its.c @@ -2024,18 +2024,22 @@ out: return ret; } -static u32 compute_next_devid_offset(struct list_head *h, +static u32 compute_next_devid_offset(struct vgic_its *its, u64 baser, struct its_device *dev) { - struct its_device *next; - u32 next_offset; + struct its_device *next = dev; - if (list_is_last(&dev->dev_list, h)) - return 0; - next = list_next_entry(dev, dev_list); - next_offset = next->device_id - dev->device_id; + /* + * Point at the next device vgic_its_save_device_tables() saves. It + * sorts device_list first, so the subtraction cannot underflow. + */ + list_for_each_entry_continue(next, &its->device_list, dev_list) { + if (vgic_its_check_id(its, baser, next->device_id, NULL)) + return min_t(u32, next->device_id - dev->device_id, + VITS_DTE_MAX_DEVID_OFFSET); + } - return min_t(u32, next_offset, VITS_DTE_MAX_DEVID_OFFSET); + return 0; } static u32 compute_next_eventid_offset(struct list_head *h, struct its_ite *ite) @@ -2276,17 +2280,18 @@ static int vgic_its_restore_itt(struct vgic_its *its, struct its_device *dev) * vgic_its_save_dte - Save a device table entry at a given GPA * * @its: ITS handle + * @baser: GITS_BASER the caller is saving against * @dev: ITS device * @ptr: GPA */ -static int vgic_its_save_dte(struct vgic_its *its, struct its_device *dev, - gpa_t ptr) +static int vgic_its_save_dte(struct vgic_its *its, u64 baser, + struct its_device *dev, gpa_t ptr) { u64 val, itt_addr_field; u32 next_offset; itt_addr_field = dev->itt_addr >> 8; - next_offset = compute_next_devid_offset(&its->device_list, dev); + next_offset = compute_next_devid_offset(its, baser, dev); val = (1ULL << KVM_ITS_DTE_VALID_SHIFT | ((u64)next_offset << KVM_ITS_DTE_NEXT_SHIFT) | (itt_addr_field << KVM_ITS_DTE_ITTADDR_SHIFT) | @@ -2385,15 +2390,16 @@ static int vgic_its_save_device_tables(struct vgic_its *its) int ret; gpa_t eaddr; + /* Don't fail a save that userspace must be able to issue. */ if (!vgic_its_check_id(its, baser, dev->device_id, &eaddr)) - return -EINVAL; + continue; ret = vgic_its_save_itt(its, dev); if (ret) return ret; - ret = vgic_its_save_dte(its, dev, eaddr); + ret = vgic_its_save_dte(its, baser, dev, eaddr); if (ret) return ret; } -- cgit v1.2.3