-----Original Message-----
From: Brost, Matthew <[email protected]>
Sent: Tuesday, December 2, 2025 9:57 AM
To: Cavitt, Jonathan <[email protected]>
Cc: [email protected]; Gupta, saurabhg <[email protected]>;
Zuo, Alex <[email protected]>; [email protected]; Zhang, Jianxun
<[email protected]>; Lin, Shuicheng <[email protected]>;
[email protected]; Wajdeczko, Michal
<[email protected]>; Mrozek, Michal <[email protected]>; Jadav,
Raag <[email protected]>; Briano, Ivan <[email protected]>; Auld,
Matthew <[email protected]>; Hirschfeld, Dafna <[email protected]>
Subject: Re: [PATCH v28 3/4] drm/xe/xe_vm: Add per VM fault info
>
> On Tue, Dec 02, 2025 at 10:47:16AM -0700, Cavitt, Jonathan wrote:
> > -----Original Message-----
> > From: Brost, Matthew <[email protected]>
> > Sent: Tuesday, December 2, 2025 9:28 AM
> > To: Cavitt, Jonathan <[email protected]>
> > Cc: [email protected]; Gupta, saurabhg
> > <[email protected]>; Zuo, Alex <[email protected]>;
> > [email protected]; Zhang, Jianxun <[email protected]>;
> > Lin, Shuicheng <[email protected]>; [email protected];
> > Wajdeczko, Michal <[email protected]>; Mrozek, Michal
> > <[email protected]>; Jadav, Raag <[email protected]>; Briano, Ivan
> > <[email protected]>; Auld, Matthew <[email protected]>;
> > Hirschfeld, Dafna <[email protected]>
> > Subject: Re: [PATCH v28 3/4] drm/xe/xe_vm: Add per VM fault info
> > >
> > > On Mon, Dec 01, 2025 at 11:55:43PM +0000, Jonathan Cavitt wrote:
> > > > Add additional information to each VM so they can report up to the first
> > > > 50 seen faults. Only pagefaults are saved this way currently, though in
> > > > the future, all faults should be tracked by the VM for future reporting.
> > > >
> > > > Additionally, of the pagefaults reported, only failed pagefaults are
> > > > saved this way, as successful pagefaults should recover silently and not
> > > > need to be reported to userspace.
> > > >
> > > > v2:
> > > > - Free vm after use (Shuicheng)
> > > > - Compress pf copy logic (Shuicheng)
> > > > - Update fault_unsuccessful before storing (Shuicheng)
> > > > - Fix old struct name in comments (Shuicheng)
> > > > - Keep first 50 pagefaults instead of last 50 (Jianxun)
> > > >
> > > > v3:
> > > > - Avoid unnecessary execution by checking MAX_PFS earlier (jcavitt)
> > > > - Fix double-locking error (jcavitt)
> > > > - Assert kmemdump is successful (Shuicheng)
> > > >
> > > > v4:
> > > > - Rename xe_vm.pfs to xe_vm.faults (jcavitt)
> > > > - Store fault data and not pagefault in xe_vm faults list (jcavitt)
> > > > - Store address, address type, and address precision per fault (jcavitt)
> > > > - Store engine class and instance data per fault (Jianxun)
> > > > - Add and fix kernel docs (Michal W)
> > > > - Properly handle kzalloc error (Michal W)
> > > > - s/MAX_PFS/MAX_FAULTS_SAVED_PER_VM (Michal W)
> > > > - Store fault level per fault (Micahl M)
> > > >
> > > > v5:
> > > > - Store fault and access type instead of address type (Jianxun)
> > > >
> > > > v6:
> > > > - Store pagefaults in non-fault-mode VMs as well (Jianxun)
> > > >
> > > > v7:
> > > > - Fix kernel docs and comments (Michal W)
> > > >
> > > > v8:
> > > > - Fix double-locking issue (Jianxun)
> > > >
> > > > v9:
> > > > - Do not report faults from reserved engines (Jianxun)
> > > >
> > > > v10:
> > > > - Remove engine class and instance (Ivan)
> > > >
> > > > v11:
> > > > - Perform kzalloc outside of lock (Auld)
> > > >
> > > > v12:
> > > > - Fix xe_vm_fault_entry kernel docs (Shuicheng)
> > > >
> > > > v13:
> > > > - Rebase and refactor (jcavitt)
> > > >
> > > > v14:
> > > > - Correctly ignore fault mode in save_pagefault_to_vm (jcavitt)
> > > >
> > > > v15:
> > > > - s/save_pagefault_to_vm/xe_pagefault_save_to_vm (Matt Brost)
> > > > - Use guard instead of spin_lock/unlock (Matt Brost)
> > > > - GT was added to xe_pagefault struct. Use xe_gt_hw_engine
> > > > instead of creating a new helper function (Matt Brost)
> > > >
> > > > Signed-off-by: Jonathan Cavitt <[email protected]>
> > > > Suggested-by: Matthew Brost <[email protected]>
> > > > Cc: Shuicheng Lin <[email protected]>
> > > > Cc: Jianxun Zhang <[email protected]>
> > > > Cc: Michal Wajdeczko <[email protected]>
> > > > Cc: Michal Mzorek <[email protected]>
> > > > Cc: Ivan Briano <[email protected]>
> > > > Cc: Matthew Auld <[email protected]>
> > > > Cc: Matthew Brost <[email protected]>
> > > > ---
> > > > drivers/gpu/drm/xe/xe_pagefault.c | 26 ++++++++++++
> > > > drivers/gpu/drm/xe/xe_vm.c | 67 +++++++++++++++++++++++++++++++
> > > > drivers/gpu/drm/xe/xe_vm.h | 9 +++++
> > > > drivers/gpu/drm/xe/xe_vm_types.h | 29 +++++++++++++
> > > > 4 files changed, 131 insertions(+)
> > > >
> > > > diff --git a/drivers/gpu/drm/xe/xe_pagefault.c
> > > > b/drivers/gpu/drm/xe/xe_pagefault.c
> > > > index 0b625a52a598..0fe092226d0a 100644
> > > > --- a/drivers/gpu/drm/xe/xe_pagefault.c
> > > > +++ b/drivers/gpu/drm/xe/xe_pagefault.c
> > > > @@ -247,6 +247,31 @@ static void xe_pagefault_print(struct xe_pagefault
> > > > *pf)
> > > > pf->consumer.engine_instance);
> > > > }
> > > >
> > > > +static void xe_pagefault_save_to_vm(struct xe_device *xe, struct
> > > > xe_pagefault *pf)
> > > > +{
> > > > + struct xe_vm *vm;
> > > > +
> > > > + /*
> > > > + * Pagefault may be asociated to VM that is not in fault mode.
> > > > + * Perform asid_to_vm behavior, except if VM is not in fault
> > > > + * mode, return VM anyways.
> > > > + */
> > > > + down_read(&xe->usm.lock);
> > > > + vm = xa_load(&xe->usm.asid_to_vm, pf->consumer.asid);
> > > > + if (vm)
> > > > + xe_vm_get(vm);
> > > > + else
> > > > + vm = ERR_PTR(-EINVAL);
> > > > + up_read(&xe->usm.lock);
> > > > +
> > > > + if (IS_ERR(vm))
> > > > + return;
> > > > +
> > > > + xe_vm_add_fault_entry_pf(vm, pf);
> > > > +
> > > > + xe_vm_put(vm);
> > > > +}
> > > > +
> > > > static void xe_pagefault_queue_work(struct work_struct *w)
> > > > {
> > > > struct xe_pagefault_queue *pf_queue =
> > > > @@ -266,6 +291,7 @@ static void xe_pagefault_queue_work(struct
> > > > work_struct *w)
> > > > err = xe_pagefault_service(&pf);
> > > > if (err) {
> > > > xe_pagefault_print(&pf);
> > > > + xe_pagefault_save_to_vm(gt_to_xe(pf.gt), &pf);
> > > > xe_gt_dbg(pf.gt, "Fault response: Unsuccessful
> > > > %pe\n",
> > > > ERR_PTR(err));
> > > > }
> > > > diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> > > > index 8ab726289583..dc6c36191274 100644
> > > > --- a/drivers/gpu/drm/xe/xe_vm.c
> > > > +++ b/drivers/gpu/drm/xe/xe_vm.c
> > > > @@ -27,6 +27,7 @@
> > > > #include "xe_device.h"
> > > > #include "xe_drm_client.h"
> > > > #include "xe_exec_queue.h"
> > > > +#include "xe_gt.h"
> > > > #include "xe_migrate.h"
> > > > #include "xe_pat.h"
> > > > #include "xe_pm.h"
> > > > @@ -578,6 +579,67 @@ static void preempt_rebind_work_func(struct
> > > > work_struct *w)
> > > > trace_xe_vm_rebind_worker_exit(vm);
> > > > }
> > > >
> > > > +/**
> > > > + * xe_vm_add_fault_entry_pf() - Add pagefault to vm fault list
> > > > + * @vm: The VM.
> > > > + * @pf: The pagefault.
> > > > + *
> > > > + * This function takes the data from the pagefault @pf and saves it to
> > > > @vm->faults.list.
> > > > + *
> > > > + * The function exits silently if the list is full, and reports a
> > > > warning if the pagefault
> > > > + * could not be saved to the list.
> > > > + */
> > > > +void xe_vm_add_fault_entry_pf(struct xe_vm *vm, struct xe_pagefault
> > > > *pf)
> > > > +{
> > > > + struct xe_vm_fault_entry *e = NULL;
> > > > + struct xe_hw_engine *hwe;
> > > > +
> > > > + /* Do not report faults on reserved engines */
> > > > + hwe = xe_gt_hw_engine(pf->gt, pf->consumer.engine_class,
> > > > + pf->consumer.engine_instance, false);
> > > > + if (!hwe || xe_hw_engine_is_reserved(hwe))
> > > > + return;
> > > > +
> > > > + e = kzalloc(sizeof(*e), GFP_KERNEL);
> > > > + if (!e) {
> > > > + drm_warn(&vm->xe->drm,
> > > > + "Could not allocate memory for fault!\n");
> > > > + return;
> > > > + }
> > > > +
> > > > + guard(spinlock)(&vm->faults.lock);
> > > > +
> > > > + /*
> > > > + * Limit the number of faults in the fault list to prevent
> > > > + * memory overuse.
> > > > + */
> > > > + if (vm->faults.len >= MAX_FAULTS_SAVED_PER_VM) {
> > > > + kfree(e);
> > > > + return;
> > > > + }
> > > > +
> > > > + e->address = pf->consumer.page_addr;
> > > > + e->address_precision = 1;
> > >
> > > Can you explain what address_precision means? It is a little unclear what
> > > '1' means here.
> >
> >
> > As I understand it, "address_precision" captures the case where the
> > page_addr in the pagefault
> > is not precisely the address accessed that caused the fault.
> >
> > For example, assume a pagefault occurred due to an access at address
> > 0x7fffce. Our current
> > implementation would report that address as a part of the pagefault
> > structure, so we would
> > return an address of 0x7fffce (as that's the reported address from the
> > pagefault), and a precision
> > of 1 (to denote the address is exact).
> >
> > By comparison, imagine if our pagefault reporting system reported the page
> > the fault occurred on
> > instead of the exact address. Or, in other words, imagine if in response
> > to a fault caused by an
> > access to address 0x7fffce, the value of pf->consumer.page_addr = 0x7ff000
> > (the page the address
> > is located on). In that case, we would return an address of 0x7ff000 (as
> > that's the reported address
> > from the pagefault), and a precision of PAGE_SIZE (to denote that the
> > pagefault occurred in the page
>
> s/PAGE_SIZE/SZ_4K - PAGE_SIZE is CPU dependent thing.
>
> We actually report faults on SZ_4K grainularity via the GuC. See
> PFD_VIRTUAL_ADDR_LO_SHIFT and how it is used. So what we likely want to
> do here is update xe_pagefault.consumer with an address precision field
> and have the GuC side populate this with 12 (if we are making this order
> based) or SZ_4K is the actual size.
We can internally store 12 to save on space, but we should report SZ_4K
to the user because it's more intuitive.
-Jonathan Cavitt
>
> Matt
>
> > and not necessarily at exactly that address).
> >
> > TL;DR: 'address' denotes a start position, and 'address_precision' denotes
> > a range. The reported
> > pagefault occurred due to an access somewhere between 'address' and
> > 'address + address_precision - 1'.
> > Since the address is exact in our case, the range is 1.
> >
> > -Jonathan Cavitt
> >
> > >
> > > Everything else LGTM.
> > >
> > > Matt
> > >
> > > > + e->access_type = pf->consumer.access_type;
> > > > + e->fault_type = pf->consumer.fault_type;
> > > > + e->fault_level = pf->consumer.fault_level;
> > > > +
> > > > + list_add_tail(&e->list, &vm->faults.list);
> > > > + vm->faults.len++;
> > > > +}
> > > > +
> > > > +static void xe_vm_clear_fault_entries(struct xe_vm *vm)
> > > > +{
> > > > + struct xe_vm_fault_entry *e, *tmp;
> > > > +
> > > > + guard(spinlock)(&vm->faults.lock);
> > > > + list_for_each_entry_safe(e, tmp, &vm->faults.list, list) {
> > > > + list_del(&e->list);
> > > > + kfree(e);
> > > > + }
> > > > + vm->faults.len = 0;
> > > > +}
> > > > +
> > > > static int xe_vma_ops_alloc(struct xe_vma_ops *vops, bool
> > > > array_of_binds)
> > > > {
> > > > int i;
> > > > @@ -1503,6 +1565,9 @@ struct xe_vm *xe_vm_create(struct xe_device *xe,
> > > > u32 flags, struct xe_file *xef)
> > > > INIT_LIST_HEAD(&vm->userptr.invalidated);
> > > > spin_lock_init(&vm->userptr.invalidated_lock);
> > > >
> > > > + INIT_LIST_HEAD(&vm->faults.list);
> > > > + spin_lock_init(&vm->faults.lock);
> > > > +
> > > > ttm_lru_bulk_move_init(&vm->lru_bulk_move);
> > > >
> > > > INIT_WORK(&vm->destroy_work, vm_destroy_work_func);
> > > > @@ -1808,6 +1873,8 @@ void xe_vm_close_and_put(struct xe_vm *vm)
> > > > }
> > > > up_write(&xe->usm.lock);
> > > >
> > > > + xe_vm_clear_fault_entries(vm);
> > > > +
> > > > for_each_tile(tile, xe, id)
> > > > xe_range_fence_tree_fini(&vm->rftree[id]);
> > > >
> > > > diff --git a/drivers/gpu/drm/xe/xe_vm.h b/drivers/gpu/drm/xe/xe_vm.h
> > > > index 361f10b3c453..e9f2de4189e0 100644
> > > > --- a/drivers/gpu/drm/xe/xe_vm.h
> > > > +++ b/drivers/gpu/drm/xe/xe_vm.h
> > > > @@ -12,6 +12,12 @@
> > > > #include "xe_map.h"
> > > > #include "xe_vm_types.h"
> > > >
> > > > +/**
> > > > + * MAX_FAULTS_SAVED_PER_VM - Maximum number of faults each vm can
> > > > store before future
> > > > + * faults are discarded to prevent memory overuse
> > > > + */
> > > > +#define MAX_FAULTS_SAVED_PER_VM 50
> > > > +
> > > > struct drm_device;
> > > > struct drm_printer;
> > > > struct drm_file;
> > > > @@ -22,6 +28,7 @@ struct dma_fence;
> > > >
> > > > struct xe_exec_queue;
> > > > struct xe_file;
> > > > +struct xe_pagefault;
> > > > struct xe_sync_entry;
> > > > struct xe_svm_range;
> > > > struct drm_exec;
> > > > @@ -309,6 +316,8 @@ void xe_vm_snapshot_capture_delayed(struct
> > > > xe_vm_snapshot *snap);
> > > > void xe_vm_snapshot_print(struct xe_vm_snapshot *snap, struct
> > > > drm_printer *p);
> > > > void xe_vm_snapshot_free(struct xe_vm_snapshot *snap);
> > > >
> > > > +void xe_vm_add_fault_entry_pf(struct xe_vm *vm, struct xe_pagefault
> > > > *pf);
> > > > +
> > > > /**
> > > > * xe_vm_set_validating() - Register this task as currently making bos
> > > > resident
> > > > * @allow_res_evict: Allow eviction of buffer objects bound to @vm when
> > > > diff --git a/drivers/gpu/drm/xe/xe_vm_types.h
> > > > b/drivers/gpu/drm/xe/xe_vm_types.h
> > > > index 3bf912bfbdcc..fff914fb0aa6 100644
> > > > --- a/drivers/gpu/drm/xe/xe_vm_types.h
> > > > +++ b/drivers/gpu/drm/xe/xe_vm_types.h
> > > > @@ -20,6 +20,7 @@
> > > > #include "xe_userptr.h"
> > > >
> > > > struct xe_bo;
> > > > +struct xe_pagefault;
> > > > struct xe_svm_range;
> > > > struct xe_sync_entry;
> > > > struct xe_user_fence;
> > > > @@ -165,6 +166,24 @@ struct xe_userptr_vma {
> > > >
> > > > struct xe_device;
> > > >
> > > > +/**
> > > > + * struct xe_vm_fault_entry - Elements of vm->faults.list
> > > > + * @list: link into @xe_vm.faults.list
> > > > + * @address: address of the fault
> > > > + * @address_precision: precision of faulted address
> > > > + * @access_type: type of address access that resulted in fault
> > > > + * @fault_type: type of fault reported
> > > > + * @fault_level: fault level of the fault
> > > > + */
> > > > +struct xe_vm_fault_entry {
> > > > + struct list_head list;
> > > > + u64 address;
> > > > + u32 address_precision;
> > > > + u8 access_type;
> > > > + u8 fault_type;
> > > > + u8 fault_level;
> > > > +};
> > > > +
> > > > struct xe_vm {
> > > > /** @gpuvm: base GPUVM used to track VMAs */
> > > > struct drm_gpuvm gpuvm;
> > > > @@ -302,6 +321,16 @@ struct xe_vm {
> > > > bool capture_once;
> > > > } error_capture;
> > > >
> > > > + /** @faults: List of all faults associated with this VM */
> > > > + struct {
> > > > + /** @faults.lock: lock protecting @faults.list */
> > > > + spinlock_t lock;
> > > > + /** @faults.list: list of xe_vm_fault_entry entries */
> > > > + struct list_head list;
> > > > + /** @faults.len: length of @faults.list */
> > > > + unsigned int len;
> > > > + } faults;
> > > > +
> > > > /**
> > > > * @validation: Validation data only valid with the vm resv
> > > > held.
> > > > * Note: This is really task state of the task holding the vm
> > > > resv,
> > > > --
> > > > 2.43.0
> > > >
> > >
>
