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Message-ID: <20250609140147.00000a1e@huawei.com>
Date: Mon, 9 Jun 2025 14:01:47 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
CC: <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<nvdimm@...ts.linux.dev>, <linux-fsdevel@...r.kernel.org>,
<linux-pm@...r.kernel.org>, Davidlohr Bueso <dave@...olabs.net>, Dave Jiang
<dave.jiang@...el.com>, Alison Schofield <alison.schofield@...el.com>, Vishal
Verma <vishal.l.verma@...el.com>, Ira Weiny <ira.weiny@...el.com>, Dan
Williams <dan.j.williams@...el.com>, Matthew Wilcox <willy@...radead.org>,
Jan Kara <jack@...e.cz>, "Rafael J . Wysocki" <rafael@...nel.org>, Len Brown
<len.brown@...el.com>, Pavel Machek <pavel@...nel.org>, Li Ming
<ming.li@...omail.com>, Jeff Johnson <jeff.johnson@....qualcomm.com>, Ying
Huang <huang.ying.caritas@...il.com>, Yao Xingtao <yaoxt.fnst@...itsu.com>,
"Peter Zijlstra" <peterz@...radead.org>, Greg KH
<gregkh@...uxfoundation.org>, Nathan Fontenot <nathan.fontenot@....com>,
Terry Bowman <terry.bowman@....com>, Robert Richter <rrichter@....com>,
"Benjamin Cheatham" <benjamin.cheatham@....com>, PradeepVineshReddy Kodamati
<PradeepVineshReddy.Kodamati@....com>, Zhijian Li <lizhijian@...itsu.com>
Subject: Re: [PATCH v4 7/7] cxl/dax: Defer DAX consumption of SOFT RESERVED
resources until after CXL region creation
On Tue, 3 Jun 2025 22:19:49 +0000
Smita Koralahalli <Smita.KoralahalliChannabasappa@....com> wrote:
> From: Nathan Fontenot <nathan.fontenot@....com>
>
> The DAX HMEM driver currently consumes all SOFT RESERVED iomem resources
> during initialization. This interferes with the CXL driver’s ability to
> create regions and trim overlapping SOFT RESERVED ranges before DAX uses
> them.
>
> To resolve this, defer the DAX driver's resource consumption if the
> cxl_acpi driver is enabled. The DAX HMEM initialization skips walking the
> iomem resource tree in this case. After CXL region creation completes,
> any remaining SOFT RESERVED resources are explicitly registered with the
> DAX driver by the CXL driver.
>
> This sequencing ensures proper handling of overlaps and fixes hotplug
> failures.
>
> Co-developed-by: Nathan Fontenot <Nathan.Fontenot@....com>
> Signed-off-by: Nathan Fontenot <Nathan.Fontenot@....com>
> Co-developed-by: Terry Bowman <terry.bowman@....com>
> Signed-off-by: Terry Bowman <terry.bowman@....com>
> Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
> ---
> drivers/cxl/core/region.c | 10 +++++++++
> drivers/dax/hmem/device.c | 43 ++++++++++++++++++++-------------------
> drivers/dax/hmem/hmem.c | 3 ++-
> include/linux/dax.h | 6 ++++++
> 4 files changed, 40 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 3a5ca44d65f3..c6c0c7ba3b20 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -10,6 +10,7 @@
> #include <linux/sort.h>
> #include <linux/idr.h>
> #include <linux/memory-tiers.h>
> +#include <linux/dax.h>
> #include <cxlmem.h>
> #include <cxl.h>
> #include "core.h"
> @@ -3553,6 +3554,11 @@ static struct resource *normalize_resource(struct resource *res)
> return NULL;
> }
>
> +static int cxl_softreserv_mem_register(struct resource *res, void *unused)
> +{
> + return hmem_register_device(phys_to_target_node(res->start), res);
> +}
> +
> static int __cxl_region_softreserv_update(struct resource *soft,
> void *_cxlr)
> {
> @@ -3590,6 +3596,10 @@ int cxl_region_softreserv_update(void)
> __cxl_region_softreserv_update);
> }
>
> + /* Now register any remaining SOFT RESERVES with DAX */
> + walk_iomem_res_desc(IORES_DESC_SOFT_RESERVED, IORESOURCE_MEM,
> + 0, -1, NULL, cxl_softreserv_mem_register);
> +
> return 0;
> }
> EXPORT_SYMBOL_NS_GPL(cxl_region_softreserv_update, "CXL");
> diff --git a/drivers/dax/hmem/device.c b/drivers/dax/hmem/device.c
> index 59ad44761191..cc1ed7bbdb1a 100644
> --- a/drivers/dax/hmem/device.c
> +++ b/drivers/dax/hmem/device.c
> @@ -8,7 +8,6 @@
> static bool nohmem;
> module_param_named(disable, nohmem, bool, 0444);
>
> -static bool platform_initialized;
> static DEFINE_MUTEX(hmem_resource_lock);
> static struct resource hmem_active = {
> .name = "HMEM devices",
> @@ -35,9 +34,7 @@ EXPORT_SYMBOL_GPL(walk_hmem_resources);
>
> static void __hmem_register_resource(int target_nid, struct resource *res)
> {
> - struct platform_device *pdev;
> struct resource *new;
> - int rc;
>
> new = __request_region(&hmem_active, res->start, resource_size(res), "",
> 0);
> @@ -47,21 +44,6 @@ static void __hmem_register_resource(int target_nid, struct resource *res)
> }
>
> new->desc = target_nid;
> -
> - if (platform_initialized)
> - return;
> -
> - pdev = platform_device_alloc("hmem_platform", 0);
> - if (!pdev) {
> - pr_err_once("failed to register device-dax hmem_platform device\n");
> - return;
> - }
> -
> - rc = platform_device_add(pdev);
> - if (rc)
> - platform_device_put(pdev);
> - else
> - platform_initialized = true;
> }
>
> void hmem_register_resource(int target_nid, struct resource *res)
> @@ -83,9 +65,28 @@ static __init int hmem_register_one(struct resource *res, void *data)
>
> static __init int hmem_init(void)
> {
> - walk_iomem_res_desc(IORES_DESC_SOFT_RESERVED,
> - IORESOURCE_MEM, 0, -1, NULL, hmem_register_one);
> - return 0;
> + struct platform_device *pdev;
> + int rc;
> +
> + if (!IS_ENABLED(CONFIG_CXL_ACPI)) {
> + walk_iomem_res_desc(IORES_DESC_SOFT_RESERVED,
> + IORESOURCE_MEM, 0, -1, NULL,
> + hmem_register_one);
> + }
> +
> + pdev = platform_device_alloc("hmem_platform", 0);
> + if (!pdev) {
> + pr_err("failed to register device-dax hmem_platform device\n");
> + return -1;
> + }
> +
> + rc = platform_device_add(pdev);
platform_device_register_simple("hmem_platform", -1, NULL, 0); or something like
that? There are quite a few variants of platform_device_register to cover
simple cases.
> + if (rc) {
> + pr_err("failed to add device-dax hmem_platform device\n");
> + platform_device_put(pdev);
> + }
> +
> + return rc;
> }
>
> /*
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