Re: [PATCH] drm/amdkfd: use iosys_map for CWSR buffer access

["Kuehling, Felix" <felix.kuehling@amd.com>]

On 2026-06-28 20:50, James Zhu wrote:
> After moving TBA/TMA from GTT to VRAM for GFX9.4.2+ in commit
> 5088a1ba6d6d, direct pointer dereferences to CWSR buffers became
> unsafe because VRAM is accessed via MMIO (PCI BAR mappings).
>
> Direct writes like 'tma[2] = enabled' and memcpy() can fail or
> produce incorrect results on non-x86 architectures because:
> - MMIO requires specific accessor functions (writeq/readq)
> - Compiler optimizations may generate invalid instruction sequences
> - No guarantee of proper memory barriers or atomic access
>
> This patch converts CWSR buffer access to use struct iosys_map,
> which automatically handles both system memory (GTT) and MMIO
> (VRAM) correctly by:
> - Using writeq/writel/memcpy_toio for MMIO regions
> - Using WRITE_ONCE/memcpy for system memory
> - Providing proper memory barriers and access guarantees
>
> Changes:
> - Replace void *cwsr_kaddr with struct iosys_map cwsr_map
> - Detect MMIO vs system memory using TTM_BO_MAP_IOMEM_MASK
> - Use iosys_map_wr() for writing trap handler addresses and flags
> - Use iosys_map_memcpy_to() for copying CWSR ISA code
>
> This ensures correct operation on all architectures while maintaining
> backward compatibility with older GPUs and APUs that use GTT.
>
> Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
> Co-Authored-By: Yifan Zhang <yifan1.zhang@amd.com>
> Signed-off-by: James Zhu <James.Zhu@amd.com>

Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>


> ---
>   drivers/gpu/drm/amd/amdkfd/kfd_priv.h    |  3 +-
>   drivers/gpu/drm/amd/amdkfd/kfd_process.c | 63 +++++++++++++++++-------
>   2 files changed, 47 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_priv.h b/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
> index ad4897f094a2..6e559aab4009 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
> @@ -32,6 +32,7 @@
>   #include <linux/atomic.h>
>   #include <linux/workqueue.h>
>   #include <linux/spinlock.h>
> +#include <linux/iosys-map.h>
>   #include <uapi/linux/kfd_ioctl.h>
>   #include <linux/idr.h>
>   #include <linux/kfifo.h>
> @@ -710,7 +711,7 @@ struct qcm_process_device {
>   
>   	/* CWSR memory */
>   	struct kgd_mem *cwsr_mem;
> -	void *cwsr_kaddr;
> +	struct iosys_map cwsr_map;
>   	uint64_t cwsr_base;
>   	uint64_t tba_addr;
>   	uint64_t tma_addr;
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_process.c b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
> index 8e701dcda8ec..7fd65c31afa2 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_process.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
> @@ -33,6 +33,7 @@
>   #include <linux/mman.h>
>   #include <linux/file.h>
>   #include <linux/pm_runtime.h>
> +#include <drm/ttm/ttm_bo.h>
>   #include "amdgpu_amdkfd.h"
>   #include "amdgpu.h"
>   #include "amdgpu_reset.h"
> @@ -745,6 +746,21 @@ static void kfd_process_free_gpuvm(struct kgd_mem *mem,
>   					       NULL);
>   }
>   
> +static void kfd_process_free_gpuvm_map(struct kgd_mem *mem,
> +			struct kfd_process_device *pdd, struct iosys_map *map)
> +{
> +	struct kfd_node *dev = pdd->dev;
> +
> +	if (map && !iosys_map_is_null(map)) {
> +		amdgpu_amdkfd_gpuvm_unmap_bo_from_kernel(mem);
> +		iosys_map_clear(map);
> +	}
> +
> +	amdgpu_amdkfd_gpuvm_unmap_memory_from_gpu(dev->adev, mem, pdd->drm_priv);
> +	amdgpu_amdkfd_gpuvm_free_memory_of_gpu(dev->adev, mem, pdd->drm_priv,
> +					       NULL);
> +}
> +
>   /* kfd_process_alloc_gpuvm - Allocate GPU VM for the KFD process
>    *	This function should be only called right after the process
>    *	is created and when kfd_processes_mutex is still being held
> @@ -1192,8 +1208,8 @@ static void kfd_process_destroy_pdds(struct kfd_process *p)
>   		if (pdd->drm_file)
>   			fput(pdd->drm_file);
>   
> -		if (pdd->qpd.cwsr_kaddr && !pdd->qpd.cwsr_base)
> -			free_pages((unsigned long)pdd->qpd.cwsr_kaddr,
> +		if (!iosys_map_is_null(&pdd->qpd.cwsr_map) && !pdd->qpd.cwsr_base)
> +			free_pages((unsigned long)pdd->qpd.cwsr_map.vaddr,
>   				get_order(KFD_CWSR_TBA_TMA_SIZE));
>   
>   		idr_destroy(&pdd->alloc_idr);
> @@ -1501,7 +1517,7 @@ static int kfd_process_device_init_cwsr_dgpu(struct kfd_process_device *pdd)
>   	void *kaddr;
>   	int ret;
>   
> -	if (!dev->kfd->cwsr_enabled || qpd->cwsr_kaddr || !qpd->cwsr_base)
> +	if (!dev->kfd->cwsr_enabled || !iosys_map_is_null(&qpd->cwsr_map) || !qpd->cwsr_base)
>   		return 0;
>   
>   	if (KFD_GC_VERSION(dev) >= IP_VERSION(9, 4, 2) && !dev->adev->apu_prefer_gtt)
> @@ -1516,17 +1532,28 @@ static int kfd_process_device_init_cwsr_dgpu(struct kfd_process_device *pdd)
>   		return ret;
>   
>   	qpd->cwsr_mem = mem;
> -	qpd->cwsr_kaddr = kaddr;
> +
> +	/* Set up iosys_map based on whether memory is MMIO or system memory */
> +	if (mem->bo->kmap.bo_kmap_type & TTM_BO_MAP_IOMEM_MASK)
> +		iosys_map_set_vaddr_iomem(&qpd->cwsr_map, kaddr);
> +	else
> +		iosys_map_set_vaddr(&qpd->cwsr_map, kaddr);
> +
>   	qpd->tba_addr = qpd->cwsr_base;
>   
> -	memcpy(qpd->cwsr_kaddr, dev->kfd->cwsr_isa, dev->kfd->cwsr_isa_size);
> +	/* Copy CWSR ISA to buffer using appropriate accessor */
> +	iosys_map_memcpy_to(&qpd->cwsr_map, 0, dev->kfd->cwsr_isa,
> +			    dev->kfd->cwsr_isa_size);
>   
>   	kfd_process_set_trap_debug_flag(&pdd->qpd,
>   					pdd->process->debug_trap_enabled);
>   
>   	qpd->tma_addr = qpd->tba_addr + KFD_CWSR_TMA_OFFSET;
> -	pr_debug("set tba :0x%llx, tma:0x%llx, cwsr_kaddr:%p for pqm.\n",
> -		 qpd->tba_addr, qpd->tma_addr, qpd->cwsr_kaddr);
> +	pr_debug("set tba :0x%llx, tma:0x%llx, cwsr_map:%s at %p for pqm.\n",
> +		 qpd->tba_addr, qpd->tma_addr,
> +		 qpd->cwsr_map.is_iomem ? "iomem" : "system",
> +		 qpd->cwsr_map.is_iomem ? (void *)qpd->cwsr_map.vaddr_iomem :
> +					  qpd->cwsr_map.vaddr);
>   
>   	return 0;
>   }
> @@ -1536,24 +1563,24 @@ static void kfd_process_device_destroy_cwsr_dgpu(struct kfd_process_device *pdd)
>   	struct kfd_node *dev = pdd->dev;
>   	struct qcm_process_device *qpd = &pdd->qpd;
>   
> -	if (!dev->kfd->cwsr_enabled || !qpd->cwsr_kaddr || !qpd->cwsr_base)
> +	if (!dev->kfd->cwsr_enabled || iosys_map_is_null(&qpd->cwsr_map) || !qpd->cwsr_base)
>   		return;
>   
> -	kfd_process_free_gpuvm(qpd->cwsr_mem, pdd, &qpd->cwsr_kaddr);
> +	kfd_process_free_gpuvm_map(qpd->cwsr_mem, pdd, &qpd->cwsr_map);
>   }
>   
>   void kfd_process_set_trap_handler(struct qcm_process_device *qpd,
>   				  uint64_t tba_addr,
>   				  uint64_t tma_addr)
>   {
> -	if (qpd->cwsr_kaddr) {
> +	if (!iosys_map_is_null(&qpd->cwsr_map)) {
>   		/* KFD trap handler is bound, record as second-level TBA/TMA
>   		 * in first-level TMA. First-level trap will jump to second.
>   		 */
> -		uint64_t *tma =
> -			(uint64_t *)(qpd->cwsr_kaddr + KFD_CWSR_TMA_OFFSET);
> -		tma[0] = tba_addr;
> -		tma[1] = tma_addr;
> +		iosys_map_wr(&qpd->cwsr_map, KFD_CWSR_TMA_OFFSET,
> +			     uint64_t, tba_addr);
> +		iosys_map_wr(&qpd->cwsr_map, KFD_CWSR_TMA_OFFSET + sizeof(uint64_t),
> +			     uint64_t, tma_addr);
>   	} else {
>   		/* No trap handler bound, bind as first-level TBA/TMA. */
>   		qpd->tba_addr = tba_addr;
> @@ -1619,10 +1646,10 @@ bool kfd_process_xnack_mode(struct kfd_process *p, bool supported)
>   void kfd_process_set_trap_debug_flag(struct qcm_process_device *qpd,
>   				     bool enabled)
>   {
> -	if (qpd->cwsr_kaddr) {
> -		uint64_t *tma =
> -			(uint64_t *)(qpd->cwsr_kaddr + KFD_CWSR_TMA_OFFSET);
> -		tma[2] = enabled;
> +	if (!iosys_map_is_null(&qpd->cwsr_map)) {
> +		iosys_map_wr(&qpd->cwsr_map,
> +			     KFD_CWSR_TMA_OFFSET + 2 * sizeof(uint64_t),
> +			     uint64_t, enabled);
>   	}
>   }
>