Re: [PATCH v3 02/36] drm/xe/vf: Lock querying GGTT config during driver init

["Lis, Tomasz" <tomasz.lis@intel.com>]

On 9/29/2025 2:15 PM, Matthew Brost wrote:
> On Mon, Sep 29, 2025 at 09:42:55AM +0200, Michal Wajdeczko wrote:
>>
>> On 9/29/2025 4:55 AM, Matthew Brost wrote:
>>> From: Tomasz Lis <tomasz.lis@intel.com>
>>>
>>> Protect access to GGTT config as this is non-static information.
>>>
>>> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
>>> Signed-off-by: Tomasz Lis <tomasz.lis@intel.com>
>>> ---
>>>   drivers/gpu/drm/xe/xe_gt_sriov_vf.c       | 96 ++++++++++++++++++-----
>>>   drivers/gpu/drm/xe/xe_gt_sriov_vf_types.h |  3 +
>>>   drivers/gpu/drm/xe/xe_sriov_vf.c          |  6 ++
>>>   3 files changed, 84 insertions(+), 21 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/xe/xe_gt_sriov_vf.c b/drivers/gpu/drm/xe/xe_gt_sriov_vf.c
>>> index 0461d5513487..016c867e5e2b 100644
>>> --- a/drivers/gpu/drm/xe/xe_gt_sriov_vf.c
>>> +++ b/drivers/gpu/drm/xe/xe_gt_sriov_vf.c
>>> @@ -440,18 +440,21 @@ static int vf_get_ggtt_info(struct xe_gt *gt)
>>>   
>>>   	xe_gt_assert(gt, IS_SRIOV_VF(gt_to_xe(gt)));
>>>   
>>> +	down_write(&config->lock);
>>> +
>> still didn't get answer to my earlier question [1]
>>
>> [1] https://patchwork.freedesktop.org/patch/676375/?series=154627&rev=2#comment_1240924
>>
> Again, this isn't a patch, so I believe Tomasz will need to chime in to
> provide an answer or conclusion here.
Now answered.
>
>>>   	err = guc_action_query_single_klv64(guc, GUC_KLV_VF_CFG_GGTT_START_KEY, &start);
>>>   	if (unlikely(err))
>>> -		return err;
>>> +		goto out;
>>>   
>>>   	err = guc_action_query_single_klv64(guc, GUC_KLV_VF_CFG_GGTT_SIZE_KEY, &size);
>>>   	if (unlikely(err))
>>> -		return err;
>>> +		goto out;
>>>   
>>>   	if (config->ggtt_size && config->ggtt_size != size) {
>>>   		xe_gt_sriov_err(gt, "Unexpected GGTT reassignment: %lluK != %lluK\n",
>>>   				size / SZ_1K, config->ggtt_size / SZ_1K);
>>> -		return -EREMCHG;
>>> +		err = -EREMCHG;
>>> +		goto out;
>>>   	}
>>>   
>>>   	xe_gt_sriov_dbg_verbose(gt, "GGTT %#llx-%#llx = %lluK\n",
>>> @@ -460,8 +463,11 @@ static int vf_get_ggtt_info(struct xe_gt *gt)
>>>   	config->ggtt_shift = start - (s64)config->ggtt_base;
>>>   	config->ggtt_base = start;
>>>   	config->ggtt_size = size;
>>> +	err = config->ggtt_size ? 0 : -ENODATA;
>>>   
>>> -	return config->ggtt_size ? 0 : -ENODATA;
>>> +out:
>>> +	up_write(&config->lock);
>>> +	return err;
>>>   }
>>>   
>>>   static int vf_get_lmem_info(struct xe_gt *gt)
>>> @@ -474,22 +480,28 @@ static int vf_get_lmem_info(struct xe_gt *gt)
>>>   
>>>   	xe_gt_assert(gt, IS_SRIOV_VF(gt_to_xe(gt)));
>>>   
>>> +	down_write(&config->lock);
>>> +
>> also, commit message says "Protect access to GGTT config "
>> while the patch seems to apply locking to the whole config ...
>>
>> what's the rationale to extend this protection?
>> just unification?

That's true, the title doesn't match.

During post-migration recovery we call the whole 
`xe_gt_sriov_vf_query_config()`, which was the main reason I went for 
protecting the whole provisioning.

Since we can query GuC multiple times, narrowing the protection would 
work as well - it would just be a bit unusual to allow two threads a 
race over writing provisioning info.

But since these values never change, both would write the same, so no 
visible problem.

If you want, I can remove the protection of anything other than GGTT. 
The solution would be then a little confusing maybe, but would work the 
same.

So, which way do we go? Fix patch name+comment, or fix locking range?

>>
>>>   	err = guc_action_query_single_klv64(guc, GUC_KLV_VF_CFG_LMEM_SIZE_KEY, &size);
>>>   	if (unlikely(err))
>>> -		return err;
>>> +		goto out;
>>>   
>>>   	if (config->lmem_size && config->lmem_size != size) {
>>>   		xe_gt_sriov_err(gt, "Unexpected LMEM reassignment: %lluM != %lluM\n",
>>>   				size / SZ_1M, config->lmem_size / SZ_1M);
>>> -		return -EREMCHG;
>>> +		err = -EREMCHG;
>>> +		goto out;
>>>   	}
>>>   
>>>   	string_get_size(size, 1, STRING_UNITS_2, size_str, sizeof(size_str));
>>>   	xe_gt_sriov_dbg_verbose(gt, "LMEM %lluM %s\n", size / SZ_1M, size_str);
>>>   
>>>   	config->lmem_size = size;
>>> +	err = config->lmem_size ? 0 : -ENODATA;
>>>   
>>> -	return config->lmem_size ? 0 : -ENODATA;
>>> +out:
>>> +	up_write(&config->lock);
>>> +	return err;
>>>   }
>>>   
>>>   static int vf_get_submission_cfg(struct xe_gt *gt)
>>> @@ -501,23 +513,27 @@ static int vf_get_submission_cfg(struct xe_gt *gt)
>>>   
>>>   	xe_gt_assert(gt, IS_SRIOV_VF(gt_to_xe(gt)));
>>>   
>>> +	down_write(&config->lock);
>>> +
>>>   	err = guc_action_query_single_klv32(guc, GUC_KLV_VF_CFG_NUM_CONTEXTS_KEY, &num_ctxs);
>>>   	if (unlikely(err))
>>> -		return err;
>>> +		goto out;
>>>   
>>>   	err = guc_action_query_single_klv32(guc, GUC_KLV_VF_CFG_NUM_DOORBELLS_KEY, &num_dbs);
>>>   	if (unlikely(err))
>>> -		return err;
>>> +		goto out;
>>>   
>>>   	if (config->num_ctxs && config->num_ctxs != num_ctxs) {
>>>   		xe_gt_sriov_err(gt, "Unexpected CTXs reassignment: %u != %u\n",
>>>   				num_ctxs, config->num_ctxs);
>>> -		return -EREMCHG;
>>> +		err = -EREMCHG;
>>> +		goto out;
>>>   	}
>>>   	if (config->num_dbs && config->num_dbs != num_dbs) {
>>>   		xe_gt_sriov_err(gt, "Unexpected DBs reassignment: %u != %u\n",
>>>   				num_dbs, config->num_dbs);
>>> -		return -EREMCHG;
>>> +		err = -EREMCHG;
>>> +		goto out;
>>>   	}
>>>   
>>>   	xe_gt_sriov_dbg_verbose(gt, "CTXs %u DBs %u\n", num_ctxs, num_dbs);
>>> @@ -525,7 +541,11 @@ static int vf_get_submission_cfg(struct xe_gt *gt)
>>>   	config->num_ctxs = num_ctxs;
>>>   	config->num_dbs = num_dbs;
>>>   
>>> -	return config->num_ctxs ? 0 : -ENODATA;
>>> +	err = config->num_ctxs ? 0 : -ENODATA;
>>> +
>>> +out:
>>> +	up_write(&config->lock);
>>> +	return err;
>>>   }
>>>   
>>>   static void vf_cache_gmdid(struct xe_gt *gt)
>>> @@ -579,11 +599,18 @@ int xe_gt_sriov_vf_query_config(struct xe_gt *gt)
>>>    */
>>>   u16 xe_gt_sriov_vf_guc_ids(struct xe_gt *gt)
>>>   {
>>> +	struct xe_gt_sriov_vf_selfconfig *config = &gt->sriov.vf.self_config;
>>> +	u16 val;
>>> +
>>>   	xe_gt_assert(gt, IS_SRIOV_VF(gt_to_xe(gt)));
>>>   	xe_gt_assert(gt, gt->sriov.vf.guc_version.major);
>>> -	xe_gt_assert(gt, gt->sriov.vf.self_config.num_ctxs);
>>>   
>>> -	return gt->sriov.vf.self_config.num_ctxs;
>>> +	down_read(&config->lock);
>>> +	xe_gt_assert(gt, config->num_ctxs);
>>> +	val = config->num_ctxs;
>>> +	up_read(&config->lock);
>>> +
>>> +	return val;
>>>   }
>>>   
>>>   /**
>>> @@ -596,11 +623,18 @@ u16 xe_gt_sriov_vf_guc_ids(struct xe_gt *gt)
>>>    */
>>>   u64 xe_gt_sriov_vf_lmem(struct xe_gt *gt)
>>>   {
>>> +	struct xe_gt_sriov_vf_selfconfig *config = &gt->sriov.vf.self_config;
>>> +	u64 val;
>>> +
>>>   	xe_gt_assert(gt, IS_SRIOV_VF(gt_to_xe(gt)));
>>>   	xe_gt_assert(gt, gt->sriov.vf.guc_version.major);
>>> -	xe_gt_assert(gt, gt->sriov.vf.self_config.lmem_size);
>>>   
>>> -	return gt->sriov.vf.self_config.lmem_size;
>>> +	down_read(&config->lock);
>>> +	xe_gt_assert(gt, config->lmem_size);
>>> +	val = config->lmem_size;
>>> +	up_read(&config->lock);
>>> +
>>> +	return val;
>>>   }
>>>   
>>>   /**
>>> @@ -613,11 +647,17 @@ u64 xe_gt_sriov_vf_lmem(struct xe_gt *gt)
>>>    */
>>>   u64 xe_gt_sriov_vf_ggtt(struct xe_gt *gt)
>>>   {
>>> +	struct xe_gt_sriov_vf_selfconfig *config = &gt->sriov.vf.self_config;
>>> +	u64 val;
>>> +
>>>   	xe_gt_assert(gt, IS_SRIOV_VF(gt_to_xe(gt)));
>>>   	xe_gt_assert(gt, gt->sriov.vf.guc_version.major);
>>> -	xe_gt_assert(gt, gt->sriov.vf.self_config.ggtt_size);
>>>   
>>> -	return gt->sriov.vf.self_config.ggtt_size;
>>> +	down_read(&config->lock);
>>> +	val = config->ggtt_size;
>>> +	up_read(&config->lock);
>>> +
>>> +	return val;
>>>   }
>>>   
>>>   /**
>>> @@ -630,11 +670,18 @@ u64 xe_gt_sriov_vf_ggtt(struct xe_gt *gt)
>>>    */
>>>   u64 xe_gt_sriov_vf_ggtt_base(struct xe_gt *gt)
>>>   {
>>> +	struct xe_gt_sriov_vf_selfconfig *config = &gt->sriov.vf.self_config;
>>> +	u64 val;
>>> +
>>>   	xe_gt_assert(gt, IS_SRIOV_VF(gt_to_xe(gt)));
>>>   	xe_gt_assert(gt, gt->sriov.vf.guc_version.major);
>>> -	xe_gt_assert(gt, gt->sriov.vf.self_config.ggtt_size);
>>>   
>>> -	return gt->sriov.vf.self_config.ggtt_base;
>>> +	down_read(&config->lock);
>>> +	xe_gt_assert(gt, config->ggtt_size);
>>> +	val = config->ggtt_base;
>>> +	up_read(&config->lock);
>>> +
>>> +	return val;
>>>   }
>>>   
>>>   /**
>>> @@ -648,11 +695,16 @@ u64 xe_gt_sriov_vf_ggtt_base(struct xe_gt *gt)
>>>   s64 xe_gt_sriov_vf_ggtt_shift(struct xe_gt *gt)
>>>   {
>>>   	struct xe_gt_sriov_vf_selfconfig *config = &gt->sriov.vf.self_config;
>>> +	s64 val;
>>>   
>>>   	xe_gt_assert(gt, IS_SRIOV_VF(gt_to_xe(gt)));
>>>   	xe_gt_assert(gt, xe_gt_is_main_type(gt));
>>>   
>>> -	return config->ggtt_shift;
>>> +	down_read(&config->lock);
>>> +	val = config->ggtt_shift;
>>> +	up_read(&config->lock);
>>> +
>>> +	return val;
>>>   }
>>>   
>>>   static int relay_action_handshake(struct xe_gt *gt, u32 *major, u32 *minor)
>>> @@ -1044,6 +1096,7 @@ void xe_gt_sriov_vf_print_config(struct xe_gt *gt, struct drm_printer *p)
>>>   
>>>   	xe_gt_assert(gt, IS_SRIOV_VF(gt_to_xe(gt)));
>>>   
>>> +	down_read(&config->lock);
>>>   	drm_printf(p, "GGTT range:\t%#llx-%#llx\n",
>>>   		   config->ggtt_base,
>>>   		   config->ggtt_base + config->ggtt_size - 1);
>>> @@ -1060,6 +1113,7 @@ void xe_gt_sriov_vf_print_config(struct xe_gt *gt, struct drm_printer *p)
>>>   
>>>   	drm_printf(p, "GuC contexts:\t%u\n", config->num_ctxs);
>>>   	drm_printf(p, "GuC doorbells:\t%u\n", config->num_dbs);
>>> +	up_read(&config->lock);
>>>   }
>>>   
>>>   /**
>>> diff --git a/drivers/gpu/drm/xe/xe_gt_sriov_vf_types.h b/drivers/gpu/drm/xe/xe_gt_sriov_vf_types.h
>>> index 298dedf4b009..d95857bd789b 100644
>>> --- a/drivers/gpu/drm/xe/xe_gt_sriov_vf_types.h
>>> +++ b/drivers/gpu/drm/xe/xe_gt_sriov_vf_types.h
>>> @@ -6,6 +6,7 @@
>>>   #ifndef _XE_GT_SRIOV_VF_TYPES_H_
>>>   #define _XE_GT_SRIOV_VF_TYPES_H_
>>>   
>>> +#include <linux/rwsem.h>
>>>   #include <linux/types.h>
>>>   #include "xe_uc_fw_types.h"
>>>   
>>> @@ -25,6 +26,8 @@ struct xe_gt_sriov_vf_selfconfig {
>>>   	u16 num_ctxs;
>>>   	/** @num_dbs: assigned number of GuC doorbells IDs. */
>>>   	u16 num_dbs;
>>> +	/** @lock: lock for protecting access to all selfconfig fields. */
>>> +	struct rw_semaphore lock;
>>>   };
>>>   
>>>   /**
>>> diff --git a/drivers/gpu/drm/xe/xe_sriov_vf.c b/drivers/gpu/drm/xe/xe_sriov_vf.c
>>> index cdd9f8e78b2a..d6e2ed9b9bbc 100644
>>> --- a/drivers/gpu/drm/xe/xe_sriov_vf.c
>>> +++ b/drivers/gpu/drm/xe/xe_sriov_vf.c
>>> @@ -197,6 +197,12 @@ static void vf_migration_init_early(struct xe_device *xe)
>>>    */
>>>   void xe_sriov_vf_init_early(struct xe_device *xe)
>>>   {
>>> +	struct xe_gt *gt;
>>> +	unsigned int id;
>>> +
>>> +	for_each_gt(gt, xe, id)
>>> +		init_rwsem(&gt->sriov.vf.self_config.lock);
>> as before, this should be done in
>>
>> 	xe_gt_sriov_vf_init_early
>>
> I pick up this change but again I think Michal's need some answers to
> his questions.
>
> Matt

Sure, that is also very early call so we can move it there. (As Matt 
actually did, just not in this patch.)

-Tomasz

>
>>> +
>>>   	vf_migration_init_early(xe);
>>>   }
>>>