[Intel-xe] [PATCH] drm/xe: Enable scratch page when page fault is enabled
Summers, Stuart
stuart.summers at intel.com
Mon Aug 28 22:25:37 UTC 2023
On Mon, 2023-08-28 at 19:11 +0000, Chang, Yu bruce wrote:
>
>
> > -----Original Message-----
> > From: Summers, Stuart <stuart.summers at intel.com>
> > Sent: Monday, August 28, 2023 10:56 AM
> > To: intel-xe at lists.freedesktop.org; Chang, Yu bruce
> > <yu.bruce.chang at intel.com>
> > Cc: Brost, Matthew <matthew.brost at intel.com>; Welty, Brian
> > <brian.welty at intel.com>; Vishwanathapura, Niranjana
> > <niranjana.vishwanathapura at intel.com>; Zeng, Oak
> > <oak.zeng at intel.com>
> > Subject: Re: [PATCH] drm/xe: Enable scratch page when page fault is
> > enabled
> >
> > On Sat, 2023-08-26 at 00:14 +0000, Chang, Bruce wrote:
> > > i915 can use scratch page even when page fault is enabled, this
> > > patch
> > > is trying to port this feature over.
> >
> > But why? From a debug perspective maybe this is interesting, but
> > ideally the
> > failed page fault should give the app everything they need to
> > recover. Why not
> > give the onus to the application to fix the addressing problems?
> >
> You are correct that this feature was originally designed to help
> application
> to run even they had invalid VA accesses. Now this should not be a
> goal anymore.
>
> The main ask is for EU debug support, and also can be potential WA if
> there
> Is any prefetch related issue, such as L1.
I agree with what Matt B. had said. It would be nice to know why EU
debug needs this. Is there an alternate solution? If not, can we enable
this only if EU debug is active?
We also don't necessarily want a bunch of workarounds added for
potential issues we don't yet know about. That's adding undue burden on
the driver.
Thanks,
Stuart
>
> > >
> > > The current i915 solution changes page table directly which may
> > > be
> > > hard to make to upstream, so a more complex solution is needed to
> > > apply to the current Xe framework if following the existing i915
> > > solution.
> > >
> > > This patch is trying to make the minimum impact to the existing
> > > driver, but still enable the scratch page support.
> > >
> > > So, the idea is to bind a scratch vma if the page fault is from
> > > an
> > > invalid access. This patch is taking advantage of null pte at
> > > this
> > > point, we may introduce a special vma for scratch vma if needed.
> >
> > So basically we want to avoid a cat fault because the cat fault
> > doesn't give
> > enough information about the bad address? Or is there something
> > else?
> >
> > Thanks,
> > Stuart
> >
> As mentioned above, mainly for EU debugger support and any potential
> prefetch WA.
>
> The issue you mentioned should be fixed with a GuC change along with
> corresponding driver change. It is coming, but separately.
>
> Thanks,
> Bruce
>
> > > After the bind, the user app can continue to run without causing
> > > a
> > > fatal failure or reset and stop.
> > >
> > > In case the app will bind this scratch vma to a valid address, it
> > > will
> > > fail the bind, this patch will handle the failre and unbind the
> > > scrach
> > > vma[s], so that the user binding will be retried to the valid
> > > address.
> > >
> > > This patch only kicks in when there is a failure for both page
> > > fault
> > > and bind, so it should has no impact to the exiating code path.
> > > On
> > > another hand, it uses actual page tables instead of special
> > > scratch
> > > page tables, so it enables potential not to invalidate TLBs when
> > > doing
> > > unbind if all upper layer page tables are still being used.
> > >
> > > tested on new scratch igt tests which will be sent out for
> > > review.
> > >
> > > Cc: Oak Zeng <oak.zeng at intel.com>
> > > Cc: Brian Welty <brian.welty at intel.com>
> > > Cc: Niranjana Vishwanathapura
> > > <niranjana.vishwanathapura at intel.com>
> > > Cc: Stuart Summers <stuart.summers at intel.com>
> > > Cc: Matthew Brost <matthew.brost at intel.com>
> > > ---
> > > drivers/gpu/drm/xe/xe_gt_pagefault.c | 9 ++++--
> > > drivers/gpu/drm/xe/xe_vm.c | 48
> > > +++++++++++++++++++++++---
> > > --
> > > drivers/gpu/drm/xe/xe_vm.h | 2 ++
> > > 3 files changed, 49 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/xe/xe_gt_pagefault.c
> > > b/drivers/gpu/drm/xe/xe_gt_pagefault.c
> > > index b6f781b3d9d7..524b38df3d7a 100644
> > > --- a/drivers/gpu/drm/xe/xe_gt_pagefault.c
> > > +++ b/drivers/gpu/drm/xe/xe_gt_pagefault.c
> > > @@ -137,8 +137,13 @@ static int handle_pagefault(struct xe_gt
> > > *gt,
> > > struct pagefault *pf)
> > > write_locked = true;
> > > vma = lookup_vma(vm, pf->page_addr);
> > > if (!vma) {
> > > - ret = -EINVAL;
> > > - goto unlock_vm;
> > > + if (vm->flags & XE_VM_FLAG_SCRATCH_PAGE)
> > > + vma = xe_bind_scratch_vma(vm, pf-
> > > >page_addr,
> > > SZ_64K);
> > > +
> > > + if (!vma) {
> > > + ret = -EINVAL;
> > > + goto unlock_vm;
> > > + }
> > > }
> > >
> > > if (!xe_vma_is_userptr(vma) ||
> > > !xe_vma_userptr_check_repin(vma)) {
> > > diff --git a/drivers/gpu/drm/xe/xe_vm.c
> > > b/drivers/gpu/drm/xe/xe_vm.c
> > > index 389ac5ba8ddf..4c3d5d781b58 100644
> > > --- a/drivers/gpu/drm/xe/xe_vm.c
> > > +++ b/drivers/gpu/drm/xe/xe_vm.c
> > > @@ -1262,7 +1262,8 @@ struct xe_vm *xe_vm_create(struct xe_device
> > *xe,
> > > u32 flags)
> > > }
> > > }
> > >
> > > - if (flags & XE_VM_FLAG_SCRATCH_PAGE) {
> > > + if (flags & XE_VM_FLAG_SCRATCH_PAGE &&
> > > + (!(flags & XE_VM_FLAG_FAULT_MODE))) {
> > > for_each_tile(tile, xe, id) {
> > > if (!vm->pt_root[id])
> > > continue; @@ -1998,10 +1999,6 @@
> > > int
> > > xe_vm_create_ioctl(struct drm_device *dev, void *data,
> > > if (XE_IOCTL_DBG(xe, args->flags &
> > > ~ALL_DRM_XE_VM_CREATE_FLAGS))
> > > return -EINVAL;
> > >
> > > - if (XE_IOCTL_DBG(xe, args->flags &
> > > DRM_XE_VM_CREATE_SCRATCH_PAGE &&
> > > - args->flags &
> > > DRM_XE_VM_CREATE_FAULT_MODE))
> > > - return -EINVAL;
> > > -
> > > if (XE_IOCTL_DBG(xe, args->flags &
> > > DRM_XE_VM_CREATE_COMPUTE_MODE &&
> > > args->flags &
> > > DRM_XE_VM_CREATE_FAULT_MODE))
> > > return -EINVAL;
> > > @@ -2783,6 +2780,39 @@ static int __xe_vma_op_execute(struct
> > > xe_vm
> > > *vm, struct xe_vma *vma,
> > > return err;
> > > }
> > >
> > > +struct xe_vma *xe_bind_scratch_vma(struct xe_vm *vm, u64 addr,
> > > u64
> > > size)
> > > +{
> > > + struct xe_vma *vma = 0;
> > > +
> > > + if (!vm->size)
> > > + return 0;
> > > +
> > > + vma = xe_vma_create(vm, NULL, 0, addr, addr + size - 1,
> > > false, true, 0);
> > > + if (!vma)
> > > + return 0;
> > > + xe_vm_insert_vma(vm, vma);
> > > +
> > > + /* fault will handle the bind */
> > > +
> > > + return vma;
> > > +}
> > > +
> > > +int xe_unbind_scratch_vma(struct xe_vm *vm, u64 addr, u64 range)
> > > {
> > > + struct xe_vma *vma;
> > > +
> > > + vma = xe_vm_find_overlapping_vma(vm, addr, range);
> > > + if (!vma)
> > > + return -ENXIO;
> > > +
> > > + if (xe_vma_is_null(vma)) {
> > > + prep_vma_destroy(vm, vma, true);
> > > + xe_vm_unbind(vm, vma, NULL, NULL, 0, NULL, true,
> > > false);
> > > + }
> > > +
> > > + return 0;
> > > +}
> > > +
> > > static int xe_vma_op_execute(struct xe_vm *vm, struct xe_vma_op
> > > *op)
> > > {
> > > int ret = 0;
> > > @@ -3205,7 +3235,6 @@ int xe_vm_bind_ioctl(struct drm_device
> > > *dev,
> > > void *data, struct drm_file *file)
> > > err = vm_bind_ioctl_check_args(xe, args, &bind_ops,
> > > &async);
> > > if (err)
> > > return err;
> > > -
> > > if (args->exec_queue_id) {
> > > q = xe_exec_queue_lookup(xef, args-
> > > >exec_queue_id);
> > > if (XE_IOCTL_DBG(xe, !q)) { @@ -3352,10 +3381,13
> > > @@
> > > int xe_vm_bind_ioctl(struct drm_device *dev, void *data, struct
> > > drm_file *file)
> > > u64 range = bind_ops[i].range;
> > > u64 addr = bind_ops[i].addr;
> > > u32 op = bind_ops[i].op;
> > > -
> > > +retry:
> > > err = vm_bind_ioctl_lookup_vma(vm, bos[i], addr,
> > > range, op);
> > > - if (err)
> > > + if (err) {
> > > + if (!xe_unbind_scratch_vma(vm, addr,
> > > range))
> > > + goto retry;
> > > goto free_syncs;
> > > + }
> > > }
> > >
> > > for (i = 0; i < args->num_binds; ++i) { diff --git
> > > a/drivers/gpu/drm/xe/xe_vm.h b/drivers/gpu/drm/xe/xe_vm.h index
> > > 6de6e3edb24a..6447bed427b1 100644
> > > --- a/drivers/gpu/drm/xe/xe_vm.h
> > > +++ b/drivers/gpu/drm/xe/xe_vm.h
> > > @@ -212,6 +212,8 @@ int xe_vma_userptr_pin_pages(struct xe_vma
> > *vma);
> > >
> > > int xe_vma_userptr_check_repin(struct xe_vma *vma);
> > >
> > > +struct xe_vma *xe_bind_scratch_vma(struct xe_vm *vm, u64 addr,
> > > u64
> > > size);
> > > +
> > > /*
> > > * XE_ONSTACK_TV is used to size the tv_onstack array that is
> > > input
> > > * to xe_vm_lock_dma_resv() and xe_vm_unlock_dma_resv().
>
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