[PATCH] drm/xe: Fix UBSAN shift-out-of-bounds failure

[Lin, Shuicheng]

Sure. Please help reword it.
Thanks Lucas.

Best Regards
Shuicheng

> -----Original Message-----
> From: De Marchi, Lucas <lucas.demarchi at intel.com>
> Sent: Thursday, May 9, 2024 11:39 AM
> To: Lin, Shuicheng <shuicheng.lin at intel.com>
> Cc: Nirmoy Das <nirmoy.das at linux.intel.com>; intel-xe at lists.freedesktop.org;
> Das, Nirmoy <nirmoy.das at intel.com>; Brost, Matthew
> <matthew.brost at intel.com>
> Subject: Re: [PATCH] drm/xe: Fix UBSAN shift-out-of-bounds failure
> 
> On Thu, May 09, 2024 at 12:25:39AM GMT, Lin, Shuicheng wrote:
> >Thanks Nirmoy for the review.
> >
> >Hi all,
> >Anything should I do in order to get it merged?
> >Thanks.
> 
> sorry I had replied but I guess it failed to send and got saved in my drafts. I just
> sent it again.
> 
> Since it's just a commit message change, if you are ok with the reword, I can just
> do it while pushing.
> 
> Lucas De Marchi
> 
> >
> >Best Regards
> >Shuicheng
> >
> >> -----Original Message-----
> >> From: Nirmoy Das <nirmoy.das at linux.intel.com>
> >> Sent: Tuesday, May 7, 2024 11:13 PM
> >> To: Lin, Shuicheng <shuicheng.lin at intel.com>;
> >> intel-xe at lists.freedesktop.org
> >> Cc: Das, Nirmoy <nirmoy.das at intel.com>; Brost, Matthew
> >> <matthew.brost at intel.com>; De Marchi, Lucas
> >> <lucas.demarchi at intel.com>
> >> Subject: Re: [PATCH] drm/xe: Fix UBSAN shift-out-of-bounds failure
> >>
> >> +Lucas
> >>
> >> On 5/7/2024 3:04 PM, Shuicheng Lin wrote:
> >> > Here is the failure stack:
> >> > [   12.988209] ------------[ cut here ]------------
> >> > [   12.988216] UBSAN: shift-out-of-bounds in ./include/linux/log2.h:57:13
> >> > [   12.988232] shift exponent 64 is too large for 64-bit type 'long unsigned
> >> int'
> >> > [   12.988235] CPU: 4 PID: 1310 Comm: gnome-shell Tainted: G     U
> >> 6.9.0-rc6+prerelease1158+ #19
> >> > [   12.988237] Hardware name: Intel Corporation Raptor Lake Client
> >> Platform/RPL-S ADP-S DDR5 UDIMM CRB, BIOS
> >> RPLSFWI1.R00.3301.A02.2208050712 08/05/2022
> >> > [   12.988239] Call Trace:
> >> > [   12.988240]  <TASK>
> >> > [   12.988242]  dump_stack_lvl+0xd7/0xf0
> >> > [   12.988248]  dump_stack+0x10/0x20
> >> > [   12.988250]  ubsan_epilogue+0x9/0x40
> >> > [   12.988253]  __ubsan_handle_shift_out_of_bounds+0x10e/0x170
> >> > [   12.988260]  dma_resv_reserve_fences.cold+0x2b/0x48
> >> > [   12.988262]  ? ww_mutex_lock_interruptible+0x3c/0x110
> >> > [   12.988267]  drm_exec_prepare_obj+0x45/0x60 [drm_exec]
> >> > [   12.988271]  ? vm_bind_ioctl_ops_execute+0x5b/0x740 [xe]
> >> > [   12.988345]  vm_bind_ioctl_ops_execute+0x78/0x740 [xe]
> >> >
> >> > It is caused by the value 0 of parameter num_fences in function
> >> drm_exec_prepare_obj.
> >> > And lead to in function __rounddown_pow_of_two, "0 - 1" causes the
> >> > shift-
> >> out-of-bounds.
> >> > For num_fences == 0 case, drm_exec_prepare_obj is the same as
> >> > drm_exec_lock_obj in function, so call drm_exec_lock_obj instead to solve it.
> >> >
> >> > Cc: Nirmoy Das <nirmoy.das at intel.com>
> >> > Cc: Matthew Brost <matthew.brost at intel.com>
> >> > Signed-off-by: Shuicheng Lin <shuicheng.lin at intel.com>
> >>
> >> Reviewed-by: Nirmoy Das <nirmoy.das at intel.com>
> >>
> >>
> >> > ---
> >> >   drivers/gpu/drm/xe/xe_vm.c | 4 ++--
> >> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >> >
> >> > diff --git a/drivers/gpu/drm/xe/xe_vm.c
> >> > b/drivers/gpu/drm/xe/xe_vm.c index d17192c8b7de..c5b1694b292f
> >> > 100644
> >> > --- a/drivers/gpu/drm/xe/xe_vm.c
> >> > +++ b/drivers/gpu/drm/xe/xe_vm.c
> >> > @@ -2692,7 +2692,7 @@ static int vma_lock_and_validate(struct
> >> > drm_exec *exec, struct xe_vma *vma,
> >> >
> >> >   	if (bo) {
> >> >   		if (!bo->vm)
> >> > -			err = drm_exec_prepare_obj(exec, &bo->ttm.base, 0);
> >> > +			err = drm_exec_lock_obj(exec, &bo->ttm.base);
> >> >   		if (!err && validate)
> >> >   			err = xe_bo_validate(bo, xe_vma_vm(vma), true);
> >> >   	}
> >> > @@ -2777,7 +2777,7 @@ static int
> >> vm_bind_ioctl_ops_lock_and_prep(struct drm_exec *exec,
> >> >   	struct xe_vma_op *op;
> >> >   	int err;
> >> >
> >> > -	err = drm_exec_prepare_obj(exec, xe_vm_obj(vm), 0);
> >> > +	err = drm_exec_lock_obj(exec, xe_vm_obj(vm));
> >> >   	if (err)
> >> >   		return err;
> >> >