Re: [PATCH v11 07/12] cxl: Validate HDM ranges before CXL reset

[Richard Cheng]

On Wed, Sep 02, 2026 at 07:27:59AM +0800, Srirangan Madhavan wrote:
> Before reset, require cached HDM decoder state, collect enabled decoder
> ranges, and reserve them with request_mem_region(). This rejects reset
> while affected CXL memory is busy and keeps the validation stable
> through reset.
> 
> If CPU cache invalidation support is available, invalidate the affected
> ranges before reset. If the runtime backend is unavailable, continue
> after the range reservation succeeds.
> 
> Reject CXL Reset when no cached HDM decoder state is available. The reset
> path needs the cached address map to validate affected ranges and perform
> CPU cache invalidation. Also reject normalized-addressing decoders for
> now because the cached decoder range is not a system physical address.
> 
> Signed-off-by: Srirangan Madhavan <smadhavan@xxxxxxxxxx>
> ---
>  drivers/cxl/core/resource.c | 255 +++++++++++++++++++++++++++++++++++-
>  1 file changed, 254 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cxl/core/resource.c b/drivers/cxl/core/resource.c
> index 439071a5c34d..13bd0c3faf7e 100644
> --- a/drivers/cxl/core/resource.c
> +++ b/drivers/cxl/core/resource.c
> @@ -11,6 +11,8 @@
>  #include <linux/iommu.h>
>  #include <linux/jiffies.h>
>  #include <linux/kernel.h>
> +#include <linux/list.h>
> +#include <linux/memregion.h>
>  #include <linux/pci.h>
>  #include <linux/slab.h>
>  
> @@ -514,6 +516,229 @@ static const u32 cxl_reset_timeout_ms[] = {
>  #define CXL_CACHE_WBI_TIMEOUT_US 100000
>  #define CXL_CACHE_WBI_POLL_US 100
>  
> +struct cxl_hdm_range {
> +	struct list_head list;
> +	struct pci_dev *pdev;
> +	struct range hpa_range;
> +	u64 len;
> +	struct resource *res;
> +};
> +
> +struct cxl_hdm_range_context {
> +	struct list_head ranges;
> +};
> +
> +static void cxl_hdm_range_context_init(struct cxl_hdm_range_context *ctx)
> +{
> +	INIT_LIST_HEAD(&ctx->ranges);
> +}
> +
> +static void cxl_hdm_range_context_destroy(struct cxl_hdm_range_context *ctx)
> +{
> +	struct cxl_hdm_range *range, *next;
> +
> +	list_for_each_entry_safe(range, next, &ctx->ranges, list) {
> +		list_del(&range->list);
> +		if (range->res)
> +			release_mem_region(range->hpa_range.start,
> +					   resource_size(range->res));
> +		kfree(range);
> +	}
> +}
> +
> +/*
> + * Bound the range twice: request_mem_region() takes resource_size_t while
> + * cpu_cache_invalidate_memregion() takes size_t, and the two differ on
> + * 32-bit builds with CONFIG_PHYS_ADDR_T_64BIT. range_len() can also reach
> + * RESOURCE_SIZE_MAX + 1 for a full-width range, and wraps to zero when
> + * resource_size_t is 64-bit, which the !len test catches.
> + */
> +static int cxl_hdm_range_validate(struct pci_dev *pdev,
> +				  const struct range *hpa_range)
> +{
> +	u64 len = range_len(hpa_range);
> +
> +	if (!len)
> +		return -EINVAL;
> +
> +	if (hpa_range->end > RESOURCE_SIZE_MAX) {
> +		pci_err(pdev,
> +			"CXL reset range [%#llx-%#llx] exceeds resource address size\n",
> +			hpa_range->start, hpa_range->end);
> +		return -EOVERFLOW;
> +	}
> +
> +	if (len > RESOURCE_SIZE_MAX) {
> +		pci_err(pdev,
> +			"CXL reset range [%#llx-%#llx] exceeds resource size\n",
> +			hpa_range->start, hpa_range->end);
> +		return -EOVERFLOW;
> +	}
> +
> +	if (len > SIZE_MAX) {
> +		pci_err(pdev,
> +			"CXL reset range [%#llx-%#llx] exceeds cache flush size\n",
> +			hpa_range->start, hpa_range->end);
> +		return -EOVERFLOW;
> +	}
> +
> +	return 0;
> +}
> +
> +static int cxl_hdm_range_add(struct cxl_hdm_range_context *ctx,
> +			     struct pci_dev *pdev, const struct range *hpa_range)
> +{
> +	struct cxl_hdm_range *range;
> +	int rc;
> +
> +	rc = cxl_hdm_range_validate(pdev, hpa_range);
> +	if (rc)
> +		return rc;
> +
> +	list_for_each_entry(range, &ctx->ranges, list)
> +		if (range->hpa_range.start == hpa_range->start &&
> +		    range->hpa_range.end == hpa_range->end)
> +			return 0;
> +
> +	range = kzalloc_obj(*range);
> +	if (!range)
> +		return -ENOMEM;
> +
> +	range->pdev = pdev;
> +	range->hpa_range = *hpa_range;
> +	range->len = range_len(hpa_range);
> +	list_add_tail(&range->list, &ctx->ranges);
> +
> +	return 0;
> +}
> +
> +static int cxl_hdm_ranges_collect(struct cxl_hdm_range_context *ctx,
> +				  struct pci_dev *pdev)
> +{
> +	struct cxl_hdm_info *info;
> +	int rc;
> +
> +	guard(rwsem_read)(&cxl_rwsem.dpa);
> +	info = pdev->hdm;
> +	if (!info) {
> +		pci_err(pdev, "CXL HDM decoder state unavailable\n");
> +		return -ENXIO;
> +	}
> +
> +	for (int i = 0; i < info->decoder_count; i++) {
> +		struct cxl_decoder_settings *settings = &info->settings[i];
> +
> +		if (!(settings->flags & CXL_DECODER_F_ENABLE))
> +			continue;
> +
> +		/* A committed zero-size decoder maps no HPA. */
> +		if (!range_len(&settings->hpa_range))
> +			continue;
> +
> +		if (settings->flags & CXL_DECODER_F_NORMALIZED_ADDRESSING) {
> +			pci_err(pdev,
> +				"CXL reset does not support normalized address decoders\n");
> +			return -EOPNOTSUPP;
> +		}
> +
> +		rc = cxl_hdm_range_add(ctx, pdev, &settings->hpa_range);
> +		if (rc)
> +			return rc;
> +	}
> +
> +	return 0;
> +}
> +
> +static int cxl_hdm_range_request(struct cxl_hdm_range *range)
> +{
> +	struct pci_dev *pdev = range->pdev;
> +	const struct range *hpa_range = &range->hpa_range;
> +
> +	range->res = request_mem_region(hpa_range->start, range->len,
> +					"cxl_reset");


How does this function provide us the required quiescing ?
I do not see it revoking existing PFN/VFIO mapping or preventing a driver
from issueing a new access after cpu_cache_invalidate_memregion()

Want to know what prevents new CXL.mem requests between cache invalidation
and reset completion ?
It does not require the range to be offline or unmapped first ?

Best regards,
Richard Cheng.

> +	if (!range->res) {
> +		pci_err(pdev,
> +			"cannot reset while CXL memory range is busy [%#llx-%#llx]\n",
> +			hpa_range->start, hpa_range->end);
> +		return -EBUSY;
> +	}
> +
> +	return 0;
> +}
> +
> +static int cxl_hdm_ranges_request(struct cxl_hdm_range_context *ctx)
> +{
> +	struct cxl_hdm_range *range;
> +	int rc;
> +
> +	lockdep_assert_held_write(&cxl_rwsem.region);
> +
> +	list_for_each_entry(range, &ctx->ranges, list) {
> +		rc = cxl_hdm_range_request(range);
> +		if (rc)
> +			return rc;
> +	}
> +
> +	return 0;
> +}
> +
> +static int cxl_hdm_range_flush_cache(struct cxl_hdm_range *range)
> +{
> +	struct pci_dev *pdev = range->pdev;
> +	const struct range *hpa_range = &range->hpa_range;
> +	int rc;
> +
> +	rc = cpu_cache_invalidate_memregion(hpa_range->start, range->len);
> +	if (rc)
> +		pci_err(pdev,
> +			"failed to invalidate CPU cache [%#llx-%#llx]: %d\n",
> +			hpa_range->start, hpa_range->end, rc);
> +
> +	return rc;
> +}
> +
> +static int cxl_hdm_ranges_flush_cpu_caches(struct cxl_hdm_range_context *ctx,
> +					   struct pci_dev *pdev)
> +{
> +	struct cxl_hdm_range *range;
> +	int rc;
> +
> +	if (list_empty(&ctx->ranges))
> +		return 0;
> +
> +	if (!cpu_cache_has_invalidate_memregion()) {
> +		pci_warn(pdev,
> +			 "CPU cache synchronization unavailable; continuing without cache invalidation\n");
> +		return 0;
> +	}
> +
> +	list_for_each_entry(range, &ctx->ranges, list) {
> +		rc = cxl_hdm_range_flush_cache(range);
> +		if (rc)
> +			return rc;
> +	}
> +
> +	return 0;
> +}
> +
> +static int cxl_hdm_ranges_prepare(struct cxl_hdm_range_context *ctx,
> +				  struct pci_dev *pdev)
> +{
> +	int rc;
> +
> +	lockdep_assert_held_write(&cxl_rwsem.region);
> +
> +	rc = cxl_hdm_ranges_collect(ctx, pdev);
> +	if (rc)
> +		return rc;
> +
> +	rc = cxl_hdm_ranges_request(ctx);
> +	if (rc)
> +		return rc;
> +
> +	return cxl_hdm_ranges_flush_cpu_caches(ctx, pdev);
> +}
> +
>  static int cxl_reset_get_dvsec(struct pci_dev *pdev, u16 *cap_out)
>  {
>  	int dvsec, rc;
> @@ -542,6 +767,20 @@ static int cxl_reset_get_dvsec(struct pci_dev *pdev, u16 *cap_out)
>  	return dvsec;
>  }
>  
> +static bool cxl_reset_hdm_available(struct pci_dev *pdev)
> +{
> +	struct cxl_hdm_info *info;
> +
> +	/*
> +	 * pdev->hdm is owned by the PCI device and released with pci_dev, so
> +	 * reset-method probes and reset requests can test availability without
> +	 * a CXL driver bound to the device.
> +	 */
> +	guard(rwsem_read)(&cxl_rwsem.dpa);
> +	info = pdev->hdm;
> +	return info && info->hdm_size;
> +}
> +
>  #define CXL_RESET_CTRL2_CMD_MASK \
>  	(PCI_DVSEC_CXL_INIT_CACHE_WBI | PCI_DVSEC_CXL_INIT_CXL_RST)
>  
> @@ -731,7 +970,9 @@ static int cxl_reset_execute(struct pci_dev *pdev, int dvsec, u16 cap)
>  
>  int cxl_reset_function(struct pci_dev *pdev, bool probe)
>  {
> +	struct cxl_hdm_range_context range_ctx;
>  	int dvsec;
> +	int rc;
>  	u16 cap;
>  
>  	dvsec = cxl_reset_get_dvsec(pdev, &cap);
> @@ -741,5 +982,17 @@ int cxl_reset_function(struct pci_dev *pdev, bool probe)
>  	if (probe)
>  		return 0;
>  
> -	return cxl_reset_execute(pdev, dvsec, cap);
> +	if (!cxl_reset_hdm_available(pdev))
> +		return -ENOTTY;
> +
> +	cxl_hdm_range_context_init(&range_ctx);
> +
> +	scoped_guard(rwsem_write, &cxl_rwsem.region) {
> +		rc = cxl_hdm_ranges_prepare(&range_ctx, pdev);
> +		if (!rc)
> +			rc = cxl_reset_execute(pdev, dvsec, cap);
> +		cxl_hdm_range_context_destroy(&range_ctx);
> +	}
> +
> +	return rc;
>  }
> -- 
> 2.43.0
>