Re: [PATCH v6 3/9] cxl: Add reset-idle and cache flush helpers

[Dave Jiang]

On 5/28/26 1:31 AM, Srirangan Madhavan wrote:
> Add helpers to collect the CXL regions affected by a memdev reset,
> verify that those regions are idle, and invalidate CPU caches for the
> affected address ranges before reset.
> 
> A memdev can participate in an interleaved region through multiple
> endpoint decoders. Track affected regions in a temporary xarray so each
> region is checked and cache-invalidated once per reset operation.
> 
> These helpers prepare the CXL.mem data path for reset. The actual reset
> orchestration and decoder restore flow are added separately.
> 
> Signed-off-by: Srirangan Madhavan <smadhavan@xxxxxxxxxx>
> ---
>  drivers/cxl/core/pci.c | 170 +++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 170 insertions(+)
> 
> diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
> index d1f487b3d809..318744695f62 100644
> --- a/drivers/cxl/core/pci.c
> +++ b/drivers/cxl/core/pci.c
> @@ -4,9 +4,11 @@
>  #include <linux/io-64-nonatomic-lo-hi.h>
>  #include <linux/device.h>
>  #include <linux/delay.h>
> +#include <linux/memregion.h>
>  #include <linux/pci.h>
>  #include <linux/pci-doe.h>
>  #include <linux/aer.h>
> +#include <linux/xarray.h>
>  #include <cxlpci.h>
>  #include <cxlmem.h>
>  #include <cxl.h>
> @@ -926,3 +928,171 @@ int cxl_port_get_possible_dports(struct cxl_port *port)
>  
>  	return ctx.count;
>  }
> +
> +static int cxl_reset_system_ram_found(struct resource *res, void *data)
> +{
> +	return 1;
> +}

Reuse core/region.c:is_system_ram()?

DJ

> +
> +struct cxl_reset_region_context {
> +	struct xarray regions;
> +};
> +
> +static void __maybe_unused
> +cxl_reset_region_context_init(struct cxl_reset_region_context *ctx)
> +{
> +	xa_init(&ctx->regions);
> +}
> +
> +static void __maybe_unused
> +cxl_reset_region_context_destroy(struct cxl_reset_region_context *ctx)
> +{
> +	xa_destroy(&ctx->regions);
> +}
> +
> +static int cxl_reset_add_region(struct cxl_reset_region_context *ctx,
> +				struct cxl_region *cxlr)
> +{
> +	int rc;
> +
> +	if (!cxlr || !cxlr->params.res)
> +		return 0;
> +
> +	rc = xa_insert(&ctx->regions, (unsigned long)cxlr, cxlr, GFP_KERNEL);
> +
> +	/* A region may be referenced by multiple affected endpoint decoders. */
> +	return rc == -EBUSY ? 0 : rc;
> +}
> +
> +static int cxl_reset_collect_region(struct device *dev, void *data)
> +{
> +	struct cxl_reset_region_context *ctx = data;
> +	struct cxl_endpoint_decoder *cxled;
> +
> +	if (!is_endpoint_decoder(dev))
> +		return 0;
> +
> +	cxled = to_cxl_endpoint_decoder(dev);
> +	return cxl_reset_add_region(ctx, cxled->cxld.region);
> +}
> +
> +static int __maybe_unused
> +cxl_reset_collect_memdev_regions(struct cxl_reset_region_context *ctx,
> +				 struct cxl_memdev *cxlmd)
> +{
> +	struct cxl_port *endpoint;
> +
> +	if (!cxlmd || !cxlmd->cxlds)
> +		return -ENODEV;
> +
> +	endpoint = cxlmd->endpoint;
> +	if (!endpoint)
> +		return 0;
> +
> +	return device_for_each_child(&endpoint->dev, ctx,
> +				     cxl_reset_collect_region);
> +}
> +
> +static bool cxl_reset_region_has_system_ram(struct cxl_region *cxlr)
> +{
> +	struct cxl_region_params *p = &cxlr->params;
> +	int rc;
> +
> +	if (!p->res)
> +		return false;
> +
> +	rc = walk_iomem_res_desc(IORES_DESC_NONE,
> +				 IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY,
> +				 p->res->start, p->res->end, NULL,
> +				 cxl_reset_system_ram_found);
> +
> +	return rc > 0;
> +}
> +
> +static int cxl_reset_validate_region_idle(struct cxl_region *cxlr)
> +{
> +	struct resource *res = cxlr->params.res;
> +	int rc = 0;
> +
> +	lockdep_assert_held_write(&cxl_rwsem.region);
> +
> +	if (cxl_reset_region_has_system_ram(cxlr)) {
> +		dev_err(&cxlr->dev,
> +			"Cannot reset while CXL memory is online as System RAM [%pr]\n",
> +			res);
> +		return -EBUSY;
> +	}
> +
> +	if (!device_trylock(&cxlr->dev))
> +		return -EAGAIN;
> +
> +	if (cxlr->dev.driver) {
> +		dev_err(&cxlr->dev,
> +			"Cannot reset while CXL region has an active driver\n");
> +		rc = -EBUSY;
> +	}
> +
> +	device_unlock(&cxlr->dev);
> +	return rc;
> +}
> +
> +static int __maybe_unused
> +cxl_reset_validate_regions_idle(struct cxl_reset_region_context *ctx)
> +{
> +	struct cxl_region *cxlr;
> +	unsigned long index;
> +	int rc;
> +
> +	xa_for_each(&ctx->regions, index, cxlr) {
> +		rc = cxl_reset_validate_region_idle(cxlr);
> +		if (rc)
> +			return rc;
> +	}
> +
> +	return 0;
> +}
> +
> +static int cxl_reset_flush_region_cache(struct cxl_region *cxlr)
> +{
> +	struct resource *res = cxlr->params.res;
> +	int rc;
> +
> +	if (!res)
> +		return 0;
> +
> +	rc = cpu_cache_invalidate_memregion(res->start, resource_size(res));
> +	if (rc)
> +		dev_err(&cxlr->dev, "Failed to invalidate CPU cache [%pr]: %d\n",
> +			res, rc);
> +
> +	return rc;
> +}
> +
> +static int __maybe_unused
> +cxl_reset_flush_cpu_caches(struct cxl_reset_region_context *ctx)
> +{
> +	struct cxl_region *cxlr;
> +	unsigned long index;
> +	int rc;
> +
> +	if (xa_empty(&ctx->regions))
> +		return 0;
> +
> +	if (!cpu_cache_has_invalidate_memregion()) {
> +		if (IS_ENABLED(CONFIG_CXL_REGION_INVALIDATION_TEST)) {
> +			pr_info_once(
> +				"Bypassing cpu_cache_invalidate_memregion() for testing!\n");
> +			return 0;
> +		}
> +		pr_warn("Failed to synchronize CPU cache state\n");
> +		return -ENXIO;
> +	}
> +
> +	xa_for_each(&ctx->regions, index, cxlr) {
> +		rc = cxl_reset_flush_region_cache(cxlr);
> +		if (rc)
> +			return rc;
> +	}
> +
> +	return 0;
> +}