Re: [PATCH v2 1/4] kernel/resource: Introduce managed SOFT RESERVED resources

Fontenot, Nathan
2025-01-23T15:55:32Z

On 1/21/2025 11:52 PM, Fan Ni wrote:
> On Thu, Jan 16, 2025 at 11:42:05AM -0600, Nathan Fontenot wrote:
>> Introduce the ability to manage SOFT RESERVED kernel resources prior to
>> these resources being placed in the iomem resource tree. This provides
>> the ability for drivers to update SOFT RESERVED resources that intersect
>> with their memory resources.
>>
>> During boot, any resources marked as IORES_DESC_SOFT_RESERVED are placed
>> on the soft reserve resource tree. Once boot completes all resources
>> are placed on the iomem resource tree. This behavior is gated by a new
>> kernel option CONFIG_SOFT_RESERVED_MANAGED.
>>
>> As part of this update two new interfaces are added for management of
>> the SOFT RESERVED resources. The release_srmem_region_adjustable()
>> routine allows for removing pieces of SOFT RESERVED resources. The
>> the merge_srmem_resources() allows drivers to merge any remaining SOFT
>> RESERVED resources into the iomem resource tree once updatea are complete.
>>
>> Signed-off-by: Nathan Fontenot <nathan.fontenot@amd.com>
>> ---
>> include/linux/ioport.h | 9 +++++
>> kernel/resource.c | 79 +++++++++++++++++++++++++++++++++++++++---
>> lib/Kconfig | 4 +++
>> 3 files changed, 87 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/linux/ioport.h b/include/linux/ioport.h
>> index 6e9fb667a1c5..2c95cf0be45e 100644
>> --- a/include/linux/ioport.h
>> +++ b/include/linux/ioport.h
>> @@ -249,6 +249,15 @@ struct resource *lookup_resource(struct resource *root, resource_size_t start);
>> int adjust_resource(struct resource *res, resource_size_t start,
>> resource_size_t size);
>> resource_size_t resource_alignment(struct resource *res);
>> +
>> +#ifdef CONFIG_SOFT_RESERVED_MANAGED
>> +void merge_srmem_resources(void);
>> +extern void release_srmem_region_adjustable(resource_size_t start,
>> + resource_size_t size);
>> +#else
>> +static inline void merge_srmem_resources(void) { }
>> +#endif
>> +
>> static inline resource_size_t resource_size(const struct resource *res)
>> {
>> return res->end - res->start + 1;
>> diff --git a/kernel/resource.c b/kernel/resource.c
>> index a83040fde236..9db420078a3f 100644
>> --- a/kernel/resource.c
>> +++ b/kernel/resource.c
>> @@ -48,6 +48,14 @@ struct resource iomem_resource = {
>> };
>> EXPORT_SYMBOL(iomem_resource);
>>
>> +static struct resource srmem_resource = {
>> + .name = "Soft Reserved mem",
>> + .start = 0,
>> + .end = -1,
>> + .flags = IORESOURCE_MEM,
>> + .desc = IORES_DESC_SOFT_RESERVED,
>> +};
>> +
>> static DEFINE_RWLOCK(resource_lock);
>>
>> static struct resource *next_resource(struct resource *p, bool skip_children)
>> @@ -818,6 +826,19 @@ static struct resource * __insert_resource(struct resource *parent, struct resou
>> {
>> struct resource *first, *next;
>>
>> + if (IS_ENABLED(CONFIG_SOFT_RESERVED_MANAGED)) {
>> + /*
>> + * During boot SOFT RESERVED resources are placed on the srmem
>> + * resource tree. These resources may be updated later in boot,
>> + * for example see the CXL driver, prior to being merged into
>> + * the iomem resource tree.
>> + */
>> + if (system_state < SYSTEM_RUNNING &&
>> + parent == &iomem_resource &&
>> + new->desc == IORES_DESC_SOFT_RESERVED)
>> + parent = &srmem_resource;
>> + }
>> +
>> for (;; parent = first) {
>> first = __request_resource(parent, new);
>> if (!first)
>> @@ -1336,11 +1357,12 @@ void __release_region(struct resource *parent, resource_size_t start,
>> }
>> EXPORT_SYMBOL(__release_region);
>>
>> -#ifdef CONFIG_MEMORY_HOTREMOVE
>
> If CONFIG_MEMORY_HOTREMOVE not defined, it seems we do not have a
> user for release_region_adjustable as
> release_mem_region_adjustable() will not exist.

The release_region_adjustable() routine is used by by release_mem_region_adjustable()
and release_srmem_region_adjustable(). We could put the following around
release_region_adjustable() to prevent it being present when not used.

#if defined(CONFIG_MEMORY_HOTREMOVE) || defined(CONFIG_SOFT_RESERVED_MANAGED)

-Nathan

>
> Fan
>> /**
>> - * release_mem_region_adjustable - release a previously reserved memory region
>> + * release_region_adjustable - release a previously reserved memory region
>> + * @parent: resource tree to release resource from
>> * @start: resource start address
>> * @size: resource region size
>> + * @busy_check: check for IORESOURCE_BUSY
>> *
>> * This interface is intended for memory hot-delete. The requested region
>> * is released from a currently busy memory resource. The requested region
>> @@ -1356,9 +1378,11 @@ EXPORT_SYMBOL(__release_region);
>> * assumes that all children remain in the lower address entry for
>> * simplicity. Enhance this logic when necessary.
>> */
>> -void release_mem_region_adjustable(resource_size_t start, resource_size_t size)
>> +static void release_region_adjustable(struct resource *parent,
>> + resource_size_t start,
>> + resource_size_t size,
>> + bool busy_check)
>> {
>> - struct resource *parent = &iomem_resource;
>> struct resource *new_res = NULL;
>> bool alloc_nofail = false;
>> struct resource **p;
>> @@ -1395,7 +1419,7 @@ void release_mem_region_adjustable(resource_size_t start, resource_size_t size)
>> if (!(res->flags & IORESOURCE_MEM))
>> break;
>>
>> - if (!(res->flags & IORESOURCE_BUSY)) {
>> + if (busy_check && !(res->flags & IORESOURCE_BUSY)) {
>> p = &res->child;
>> continue;
>> }
>> @@ -1445,6 +1469,51 @@ void release_mem_region_adjustable(resource_size_t start, resource_size_t size)
>> write_unlock(&resource_lock);
>> free_resource(new_res);
>> }
>> +
>> +#ifdef CONFIG_SOFT_RESERVED_MANAGED
>> +/**
>> + * merge_srmem_resources - merge srmem resources into the iomem resource tree
>> + *
>> + * This is intended to allow kernel drivers that manage the SOFT RESERVED
>> + * resources to merge any remaining resources into the iomem resource tree
>> + * once any updates have been made.
>> + */
>> +void merge_srmem_resources(void)
>> +{
>> + struct resource *res, *next;
>> + int rc;
>> +
>> + for (res = srmem_resource.child; res; res = next) {
>> + next = next_resource(res, true);
>> +
>> + write_lock(&resource_lock);
>> +
>> + if (WARN_ON(__release_resource(res, true))) {
>> + write_unlock(&resource_lock);
>> + continue;
>> + }
>> +
>> + if (WARN_ON(__insert_resource(&iomem_resource, res)))
>> + __insert_resource(&srmem_resource, res);
>> +
>> + write_unlock(&resource_lock);
>> + }
>> +}
>> +EXPORT_SYMBOL_GPL(merge_srmem_resources);
>> +
>> +void release_srmem_region_adjustable(resource_size_t start,
>> + resource_size_t size)
>> +{
>> + release_region_adjustable(&srmem_resource, start, size, false);
>> +}
>> +EXPORT_SYMBOL(release_srmem_region_adjustable);
>> +#endif
>> +
>> +#ifdef CONFIG_MEMORY_HOTREMOVE
>> +void release_mem_region_adjustable(resource_size_t start, resource_size_t size)
>> +{
>> + release_region_adjustable(&iomem_resource, start, size, true);
>> +}
>> #endif /* CONFIG_MEMORY_HOTREMOVE */
>>
>> #ifdef CONFIG_MEMORY_HOTPLUG
>> diff --git a/lib/Kconfig b/lib/Kconfig
>> index b38849af6f13..4f4011334051 100644
>> --- a/lib/Kconfig
>> +++ b/lib/Kconfig
>> @@ -777,3 +777,7 @@ config POLYNOMIAL
>>
>> config FIRMWARE_TABLE
>> bool
>> +
>> +config SOFT_RESERVED_MANAGED
>> + bool
>> + default n
>> --
>> 2.43.0
>>