Re: [PATCH v2 01/34] drm/xe/vf: Lock querying GGTT config during driver init

[Michal Wajdeczko <michal.wajdeczko@intel.com>]

On 9/24/2025 3:15 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);

do we need to protect also VF2GUC communication ..

> +
>  	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;
>  

.. or just RW access to the data itself from here?

>  	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);
> +
>  	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);

the purpose of this assert was to make sure no part of the VF driver
is trying to get num_ctxs before we finish querying it from the GuC ..

>  
> -	return gt->sriov.vf.self_config.num_ctxs;
> +	down_read(&config->lock);
> +	xe_gt_assert(gt, config->num_ctxs);

.. instead of moving this assert in the middle of the lock ..

> +	val = config->num_ctxs;
> +	up_read(&config->lock);
> +

.. for code clarity you can add assert here as:

	xe_gt_assert(gt, val);
> +	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);

ditto

>  
> -	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);

this is a wrong place - VF's per-GT data shall be initialized in
the per-GT code somewhere in xe_gt_sriov_vf.c

> +
>  	vf_migration_init_early(xe);
>  }
>