diff mbox series

[33/46] resource: Introduce alloc_free_mem_region()

Message ID 20220624041950.559155-8-dan.j.williams@intel.com
State Superseded
Headers show
Series CXL PMEM Region Provisioning | expand

Commit Message

Dan Williams June 24, 2022, 4:19 a.m. UTC
The core of devm_request_free_mem_region() is a helper that searches for
free space in iomem_resource and performs __request_region_locked() on
the result of that search. The policy choices of the implementation
conform to what CONFIG_DEVICE_PRIVATE users want which is memory that is
immediately marked busy, and a preference to search for the first-fit
free range in descending order from the top of the physical address
space.

CXL has a need for a similar allocator, but with the following tweaks:

1/ Search for free space in ascending order

2/ Search for free space relative to a given CXL window

3/ 'insert' rather than 'request' the new resource given downstream
   drivers from the CXL Region driver (like the pmem or dax drivers) are
   responsible for request_mem_region() when they activate the memory
   range.

Rework __request_free_mem_region() into get_free_mem_region() which
takes a set of GFR_* (Get Free Region) flags to control the allocation
policy (ascending vs descending), and "busy" policy (insert_resource()
vs request_region()).

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/linux-cxl/20220420143406.GY2120790@nvidia.com/
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 include/linux/ioport.h |   2 +
 kernel/resource.c      | 174 ++++++++++++++++++++++++++++++++---------
 mm/Kconfig             |   5 ++
 3 files changed, 146 insertions(+), 35 deletions(-)

Comments

Jonathan Cameron June 30, 2022, 10:35 a.m. UTC | #1
On Thu, 23 Jun 2022 21:19:37 -0700
Dan Williams <dan.j.williams@intel.com> wrote:

> The core of devm_request_free_mem_region() is a helper that searches for
> free space in iomem_resource and performs __request_region_locked() on
> the result of that search. The policy choices of the implementation
> conform to what CONFIG_DEVICE_PRIVATE users want which is memory that is
> immediately marked busy, and a preference to search for the first-fit
> free range in descending order from the top of the physical address
> space.
> 
> CXL has a need for a similar allocator, but with the following tweaks:
> 
> 1/ Search for free space in ascending order
> 
> 2/ Search for free space relative to a given CXL window
> 
> 3/ 'insert' rather than 'request' the new resource given downstream
>    drivers from the CXL Region driver (like the pmem or dax drivers) are
>    responsible for request_mem_region() when they activate the memory
>    range.
> 
> Rework __request_free_mem_region() into get_free_mem_region() which
> takes a set of GFR_* (Get Free Region) flags to control the allocation
> policy (ascending vs descending), and "busy" policy (insert_resource()
> vs request_region()).
> 
> Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
> Link: https://lore.kernel.org/linux-cxl/20220420143406.GY2120790@nvidia.com/
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: Christoph Hellwig <hch@infradead.org>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

A few things inline,

Thanks,

Jonathan

> ---
>  include/linux/ioport.h |   2 +
>  kernel/resource.c      | 174 ++++++++++++++++++++++++++++++++---------
>  mm/Kconfig             |   5 ++
>  3 files changed, 146 insertions(+), 35 deletions(-)
> 
> diff --git a/include/linux/ioport.h b/include/linux/ioport.h
> index ec5f71f7135b..ed03518347aa 100644
> --- a/include/linux/ioport.h
> +++ b/include/linux/ioport.h
> @@ -329,6 +329,8 @@ struct resource *devm_request_free_mem_region(struct device *dev,
>  		struct resource *base, unsigned long size);
>  struct resource *request_free_mem_region(struct resource *base,
>  		unsigned long size, const char *name);
> +struct resource *alloc_free_mem_region(struct resource *base,
> +		unsigned long size, unsigned long align, const char *name);
>  
>  static inline void irqresource_disabled(struct resource *res, u32 irq)
>  {
> diff --git a/kernel/resource.c b/kernel/resource.c
> index 53a534db350e..9fc990274106 100644
> --- a/kernel/resource.c
> +++ b/kernel/resource.c


> +static bool gfr_continue(struct resource *base, resource_size_t addr,
> +			 resource_size_t size, unsigned long flags)
> +{
> +	if (flags & GFR_DESCENDING)
> +		return addr > size && addr >= base->start;
> +	return addr > addr - size &&

Is this checking for wrap around?  If so maybe a comment to call that out?

> +	       addr <= min_t(resource_size_t, base->end,
> +			     (1ULL << MAX_PHYSMEM_BITS) - 1);
> +}
> +
> +static resource_size_t gfr_next(resource_size_t addr, resource_size_t size,
> +				unsigned long flags)
> +{
> +	if (flags & GFR_DESCENDING)
> +		return addr - size;
> +	return addr + size;
> +}
> +
> +static void remove_free_mem_region(void *_res)
>  {
> -	resource_size_t end, addr;
> +	struct resource *res = _res;
> +
> +	if (res->parent)
> +		remove_resource(res);
> +	free_resource(res);
> +}
> +
> +static struct resource *
> +get_free_mem_region(struct device *dev, struct resource *base,
> +		    resource_size_t size, const unsigned long align,
> +		    const char *name, const unsigned long desc,
> +		    const unsigned long flags)
> +{
> +	resource_size_t addr;
>  	struct resource *res;
>  	struct region_devres *dr = NULL;
>  
> -	size = ALIGN(size, 1UL << PA_SECTION_SHIFT);
> -	end = min_t(unsigned long, base->end, (1UL << MAX_PHYSMEM_BITS) - 1);
> -	addr = end - size + 1UL;
> +	size = ALIGN(size, align);
>  
>  	res = alloc_resource(GFP_KERNEL);
>  	if (!res)
>  		return ERR_PTR(-ENOMEM);
>  
> -	if (dev) {
> +	if (dev && (flags & GFR_REQUEST_REGION)) {
>  		dr = devres_alloc(devm_region_release,
>  				sizeof(struct region_devres), GFP_KERNEL);
>  		if (!dr) {
>  			free_resource(res);
>  			return ERR_PTR(-ENOMEM);
>  		}
> +	} else if (dev) {
> +		if (devm_add_action_or_reset(dev, remove_free_mem_region, res))
> +			return ERR_PTR(-ENOMEM);

slightly nicer to return whatever value you got back from devm_add_action_or_reset()

>  	}
>  
>  	write_lock(&resource_lock);
> -	for (; addr > size && addr >= base->start; addr -= size) {
> -		if (__region_intersects(addr, size, 0, IORES_DESC_NONE) !=
> -				REGION_DISJOINT)
> +	for (addr = gfr_start(base, size, align, flags);
> +	     gfr_continue(base, addr, size, flags);
> +	     addr = gfr_next(addr, size, flags)) {
> +		if (__region_intersects(base, addr, size, 0, IORES_DESC_NONE) !=
> +		    REGION_DISJOINT)
>  			continue;
>  
> -		if (__request_region_locked(res, &iomem_resource, addr, size,
> -						name, 0))
> -			break;
> +		if (flags & GFR_REQUEST_REGION) {
> +			if (__request_region_locked(res, &iomem_resource, addr,
> +						    size, name, 0))
> +				break;
>  
> -		if (dev) {
> -			dr->parent = &iomem_resource;
> -			dr->start = addr;
> -			dr->n = size;
> -			devres_add(dev, dr);
> -		}
> +			if (dev) {
> +				dr->parent = &iomem_resource;
> +				dr->start = addr;
> +				dr->n = size;
> +				devres_add(dev, dr);
> +			}
>  
> -		res->desc = IORES_DESC_DEVICE_PRIVATE_MEMORY;
> -		write_unlock(&resource_lock);
> +			res->desc = desc;
> +			write_unlock(&resource_lock);
> +
> +
> +			/*
> +			 * A driver is claiming this region so revoke any
> +			 * mappings.
> +			 */
> +			revoke_iomem(res);
> +		} else {
> +			res->start = addr;
> +			res->end = addr + size - 1;
> +			res->name = name;
> +			res->desc = desc;
> +			res->flags = IORESOURCE_MEM;
> +
> +			/*
> +			 * Only succeed if the resource hosts an exclusive
> +			 * range after the insert
> +			 */
> +			if (__insert_resource(base, res) || res->child)
> +				break;
> +
> +			write_unlock(&resource_lock);
> +		}
>  
> -		/*
> -		 * A driver is claiming this region so revoke any mappings.
> -		 */
> -		revoke_iomem(res);
>  		return res;
>  	}
>  	write_unlock(&resource_lock);
>  
> -	free_resource(res);
> -	if (dr)
> +	if (flags & GFR_REQUEST_REGION) {
> +		free_resource(res);
>  		devres_free(dr);

The original if (dr) was unnecessary as devres_free() checks.

Looking just at this patch it looks like you aren't covering the
corner case of dev == NULL and GFR_REQUEST_REGION.

Perhaps worth a tiny comment in patch description? (doesn't seem worth
pulling this change out as a precursor given it's so small).
Of add the extra if (dr) back in to 'document' that no change...


> +	} else if (dev)
> +		devm_release_action(dev, remove_free_mem_region, res);
>  
>  	return ERR_PTR(-ERANGE);
>  }
> @@ -1854,18 +1928,48 @@ static struct resource *__request_free_mem_region(struct device *dev,
>  struct resource *devm_request_free_mem_region(struct device *dev,
>  		struct resource *base, unsigned long size)
>  {
> -	return __request_free_mem_region(dev, base, size, dev_name(dev));
> +	unsigned long flags = GFR_DESCENDING | GFR_REQUEST_REGION;
> +
> +	return get_free_mem_region(dev, base, size, GFR_DEFAULT_ALIGN,
> +				   dev_name(dev),
> +				   IORES_DESC_DEVICE_PRIVATE_MEMORY, flags);
>  }
>  EXPORT_SYMBOL_GPL(devm_request_free_mem_region);
>  
>  struct resource *request_free_mem_region(struct resource *base,
>  		unsigned long size, const char *name)
>  {
> -	return __request_free_mem_region(NULL, base, size, name);
> +	unsigned long flags = GFR_DESCENDING | GFR_REQUEST_REGION;
> +
> +	return get_free_mem_region(NULL, base, size, GFR_DEFAULT_ALIGN, name,
> +				   IORES_DESC_DEVICE_PRIVATE_MEMORY, flags);
>  }
>  EXPORT_SYMBOL_GPL(request_free_mem_region);
>  
> -#endif /* CONFIG_DEVICE_PRIVATE */
> +/**
> + * alloc_free_mem_region - find a free region relative to @base
> + * @base: resource that will parent the new resource
> + * @size: size in bytes of memory to allocate from @base
> + * @align: alignment requirements for the allocation
> + * @name: resource name
> + *
> + * Buses like CXL, that can dynamically instantiate new memory regions,
> + * need a method to allocate physical address space for those regions.
> + * Allocate and insert a new resource to cover a free, unclaimed by a
> + * descendant of @base, range in the span of @base.
> + */
> +struct resource *alloc_free_mem_region(struct resource *base,
Given the extra align parameter, does it make sense to give this a naming
that highlights that vs the other two interfaces above?

alloc_free_mem_region_aligned()

> +				       unsigned long size, unsigned long align,
> +				       const char *name)
> +{
> +	/* GFR_ASCENDING | GFR_INSERT_RESOURCE */

Given those flags don't exist and some fool like me might grep for them
perhaps better to describe it in text

	/* Default of ascending direction and insert resource */

> +	unsigned long flags = 0;
> +
> +	return get_free_mem_region(NULL, base, size, align, name,
> +				   IORES_DESC_NONE, flags);
> +}
> +EXPORT_SYMBOL_NS_GPL(alloc_free_mem_region, CXL);
> +#endif /* CONFIG_GET_FREE_REGION */
>  
>  static int __init strict_iomem(char *str)
>  {
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 169e64192e48..a5b4fee2e3fd 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -994,9 +994,14 @@ config HMM_MIRROR
>  	bool
>  	depends on MMU
>  
> +config GET_FREE_REGION
> +	depends on SPARSEMEM
> +	bool
> +
>  config DEVICE_PRIVATE
>  	bool "Unaddressable device memory (GPU memory, ...)"
>  	depends on ZONE_DEVICE
> +	select GET_FREE_REGION
>  
>  	help
>  	  Allows creation of struct pages to represent unaddressable device
Dan Williams July 10, 2022, 9:58 p.m. UTC | #2
Jonathan Cameron wrote:
> On Thu, 23 Jun 2022 21:19:37 -0700
> Dan Williams <dan.j.williams@intel.com> wrote:
> 
> > The core of devm_request_free_mem_region() is a helper that searches for
> > free space in iomem_resource and performs __request_region_locked() on
> > the result of that search. The policy choices of the implementation
> > conform to what CONFIG_DEVICE_PRIVATE users want which is memory that is
> > immediately marked busy, and a preference to search for the first-fit
> > free range in descending order from the top of the physical address
> > space.
> > 
> > CXL has a need for a similar allocator, but with the following tweaks:
> > 
> > 1/ Search for free space in ascending order
> > 
> > 2/ Search for free space relative to a given CXL window
> > 
> > 3/ 'insert' rather than 'request' the new resource given downstream
> >    drivers from the CXL Region driver (like the pmem or dax drivers) are
> >    responsible for request_mem_region() when they activate the memory
> >    range.
> > 
> > Rework __request_free_mem_region() into get_free_mem_region() which
> > takes a set of GFR_* (Get Free Region) flags to control the allocation
> > policy (ascending vs descending), and "busy" policy (insert_resource()
> > vs request_region()).
> > 
> > Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
> > Link: https://lore.kernel.org/linux-cxl/20220420143406.GY2120790@nvidia.com/
> > Cc: Matthew Wilcox <willy@infradead.org>
> > Cc: Christoph Hellwig <hch@infradead.org>
> > Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> 
> A few things inline,
> 
> Thanks,
> 
> Jonathan
> 
> > ---
> >  include/linux/ioport.h |   2 +
> >  kernel/resource.c      | 174 ++++++++++++++++++++++++++++++++---------
> >  mm/Kconfig             |   5 ++
> >  3 files changed, 146 insertions(+), 35 deletions(-)
> > 
> > diff --git a/include/linux/ioport.h b/include/linux/ioport.h
> > index ec5f71f7135b..ed03518347aa 100644
> > --- a/include/linux/ioport.h
> > +++ b/include/linux/ioport.h
> > @@ -329,6 +329,8 @@ struct resource *devm_request_free_mem_region(struct device *dev,
> >  		struct resource *base, unsigned long size);
> >  struct resource *request_free_mem_region(struct resource *base,
> >  		unsigned long size, const char *name);
> > +struct resource *alloc_free_mem_region(struct resource *base,
> > +		unsigned long size, unsigned long align, const char *name);
> >  
> >  static inline void irqresource_disabled(struct resource *res, u32 irq)
> >  {
> > diff --git a/kernel/resource.c b/kernel/resource.c
> > index 53a534db350e..9fc990274106 100644
> > --- a/kernel/resource.c
> > +++ b/kernel/resource.c
> 
> 
> > +static bool gfr_continue(struct resource *base, resource_size_t addr,
> > +			 resource_size_t size, unsigned long flags)
> > +{
> > +	if (flags & GFR_DESCENDING)
> > +		return addr > size && addr >= base->start;
> > +	return addr > addr - size &&
> 
> Is this checking for wrap around?  If so maybe a comment to call that out?

Yes, and ok.

> 
> > +	       addr <= min_t(resource_size_t, base->end,
> > +			     (1ULL << MAX_PHYSMEM_BITS) - 1);
> > +}
> > +
> > +static resource_size_t gfr_next(resource_size_t addr, resource_size_t size,
> > +				unsigned long flags)
> > +{
> > +	if (flags & GFR_DESCENDING)
> > +		return addr - size;
> > +	return addr + size;
> > +}
> > +
> > +static void remove_free_mem_region(void *_res)
> >  {
> > -	resource_size_t end, addr;
> > +	struct resource *res = _res;
> > +
> > +	if (res->parent)
> > +		remove_resource(res);
> > +	free_resource(res);
> > +}
> > +
> > +static struct resource *
> > +get_free_mem_region(struct device *dev, struct resource *base,
> > +		    resource_size_t size, const unsigned long align,
> > +		    const char *name, const unsigned long desc,
> > +		    const unsigned long flags)
> > +{
> > +	resource_size_t addr;
> >  	struct resource *res;
> >  	struct region_devres *dr = NULL;
> >  
> > -	size = ALIGN(size, 1UL << PA_SECTION_SHIFT);
> > -	end = min_t(unsigned long, base->end, (1UL << MAX_PHYSMEM_BITS) - 1);
> > -	addr = end - size + 1UL;
> > +	size = ALIGN(size, align);
> >  
> >  	res = alloc_resource(GFP_KERNEL);
> >  	if (!res)
> >  		return ERR_PTR(-ENOMEM);
> >  
> > -	if (dev) {
> > +	if (dev && (flags & GFR_REQUEST_REGION)) {
> >  		dr = devres_alloc(devm_region_release,
> >  				sizeof(struct region_devres), GFP_KERNEL);
> >  		if (!dr) {
> >  			free_resource(res);
> >  			return ERR_PTR(-ENOMEM);
> >  		}
> > +	} else if (dev) {
> > +		if (devm_add_action_or_reset(dev, remove_free_mem_region, res))
> > +			return ERR_PTR(-ENOMEM);
> 
> slightly nicer to return whatever value you got back from devm_add_action_or_reset()

Yes, but it is known to only return -ENOMEM on failure and saves adding
a local @rc variable.

> 
> >  	}
> >  
> >  	write_lock(&resource_lock);
> > -	for (; addr > size && addr >= base->start; addr -= size) {
> > -		if (__region_intersects(addr, size, 0, IORES_DESC_NONE) !=
> > -				REGION_DISJOINT)
> > +	for (addr = gfr_start(base, size, align, flags);
> > +	     gfr_continue(base, addr, size, flags);
> > +	     addr = gfr_next(addr, size, flags)) {
> > +		if (__region_intersects(base, addr, size, 0, IORES_DESC_NONE) !=
> > +		    REGION_DISJOINT)
> >  			continue;
> >  
> > -		if (__request_region_locked(res, &iomem_resource, addr, size,
> > -						name, 0))
> > -			break;
> > +		if (flags & GFR_REQUEST_REGION) {
> > +			if (__request_region_locked(res, &iomem_resource, addr,
> > +						    size, name, 0))
> > +				break;
> >  
> > -		if (dev) {
> > -			dr->parent = &iomem_resource;
> > -			dr->start = addr;
> > -			dr->n = size;
> > -			devres_add(dev, dr);
> > -		}
> > +			if (dev) {
> > +				dr->parent = &iomem_resource;
> > +				dr->start = addr;
> > +				dr->n = size;
> > +				devres_add(dev, dr);
> > +			}
> >  
> > -		res->desc = IORES_DESC_DEVICE_PRIVATE_MEMORY;
> > -		write_unlock(&resource_lock);
> > +			res->desc = desc;
> > +			write_unlock(&resource_lock);
> > +
> > +
> > +			/*
> > +			 * A driver is claiming this region so revoke any
> > +			 * mappings.
> > +			 */
> > +			revoke_iomem(res);
> > +		} else {
> > +			res->start = addr;
> > +			res->end = addr + size - 1;
> > +			res->name = name;
> > +			res->desc = desc;
> > +			res->flags = IORESOURCE_MEM;
> > +
> > +			/*
> > +			 * Only succeed if the resource hosts an exclusive
> > +			 * range after the insert
> > +			 */
> > +			if (__insert_resource(base, res) || res->child)
> > +				break;
> > +
> > +			write_unlock(&resource_lock);
> > +		}
> >  
> > -		/*
> > -		 * A driver is claiming this region so revoke any mappings.
> > -		 */
> > -		revoke_iomem(res);
> >  		return res;
> >  	}
> >  	write_unlock(&resource_lock);
> >  
> > -	free_resource(res);
> > -	if (dr)
> > +	if (flags & GFR_REQUEST_REGION) {
> > +		free_resource(res);
> >  		devres_free(dr);
> 
> The original if (dr) was unnecessary as devres_free() checks.
> 
> Looking just at this patch it looks like you aren't covering the
> corner case of dev == NULL and GFR_REQUEST_REGION.
> 
> Perhaps worth a tiny comment in patch description? (doesn't seem worth
> pulling this change out as a precursor given it's so small).
> Of add the extra if (dr) back in to 'document' that no change...

Added to the changelog:

As part of the consolidation of the legacy GFR_REQUEST_REGION case with
the new default of just inserting a new resource into the free space
some minor cleanups like not checking for NULL before calling
devres_free() (which does its own check) is included.

> 
> 
> > +	} else if (dev)
> > +		devm_release_action(dev, remove_free_mem_region, res);
> >  
> >  	return ERR_PTR(-ERANGE);
> >  }
> > @@ -1854,18 +1928,48 @@ static struct resource *__request_free_mem_region(struct device *dev,
> >  struct resource *devm_request_free_mem_region(struct device *dev,
> >  		struct resource *base, unsigned long size)
> >  {
> > -	return __request_free_mem_region(dev, base, size, dev_name(dev));
> > +	unsigned long flags = GFR_DESCENDING | GFR_REQUEST_REGION;
> > +
> > +	return get_free_mem_region(dev, base, size, GFR_DEFAULT_ALIGN,
> > +				   dev_name(dev),
> > +				   IORES_DESC_DEVICE_PRIVATE_MEMORY, flags);
> >  }
> >  EXPORT_SYMBOL_GPL(devm_request_free_mem_region);
> >  
> >  struct resource *request_free_mem_region(struct resource *base,
> >  		unsigned long size, const char *name)
> >  {
> > -	return __request_free_mem_region(NULL, base, size, name);
> > +	unsigned long flags = GFR_DESCENDING | GFR_REQUEST_REGION;
> > +
> > +	return get_free_mem_region(NULL, base, size, GFR_DEFAULT_ALIGN, name,
> > +				   IORES_DESC_DEVICE_PRIVATE_MEMORY, flags);
> >  }
> >  EXPORT_SYMBOL_GPL(request_free_mem_region);
> >  
> > -#endif /* CONFIG_DEVICE_PRIVATE */
> > +/**
> > + * alloc_free_mem_region - find a free region relative to @base
> > + * @base: resource that will parent the new resource
> > + * @size: size in bytes of memory to allocate from @base
> > + * @align: alignment requirements for the allocation
> > + * @name: resource name
> > + *
> > + * Buses like CXL, that can dynamically instantiate new memory regions,
> > + * need a method to allocate physical address space for those regions.
> > + * Allocate and insert a new resource to cover a free, unclaimed by a
> > + * descendant of @base, range in the span of @base.
> > + */
> > +struct resource *alloc_free_mem_region(struct resource *base,
> Given the extra align parameter, does it make sense to give this a naming
> that highlights that vs the other two interfaces above?
> 
> alloc_free_mem_region_aligned()

The other variants are also aligned, they just aren't variably aligned,
they are implicitly aligned to GFR_DEFAULT_ALIGN. So I think calling
this one _aligned() betrays what is happening in the other cases.

> > +				       unsigned long size, unsigned long align,
> > +				       const char *name)
> > +{
> > +	/* GFR_ASCENDING | GFR_INSERT_RESOURCE */
> 
> Given those flags don't exist and some fool like me might grep for them
> perhaps better to describe it in text
> 
> 	/* Default of ascending direction and insert resource */

Ok.
diff mbox series

Patch

diff --git a/include/linux/ioport.h b/include/linux/ioport.h
index ec5f71f7135b..ed03518347aa 100644
--- a/include/linux/ioport.h
+++ b/include/linux/ioport.h
@@ -329,6 +329,8 @@  struct resource *devm_request_free_mem_region(struct device *dev,
 		struct resource *base, unsigned long size);
 struct resource *request_free_mem_region(struct resource *base,
 		unsigned long size, const char *name);
+struct resource *alloc_free_mem_region(struct resource *base,
+		unsigned long size, unsigned long align, const char *name);
 
 static inline void irqresource_disabled(struct resource *res, u32 irq)
 {
diff --git a/kernel/resource.c b/kernel/resource.c
index 53a534db350e..9fc990274106 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -489,8 +489,9 @@  int __weak page_is_ram(unsigned long pfn)
 }
 EXPORT_SYMBOL_GPL(page_is_ram);
 
-static int __region_intersects(resource_size_t start, size_t size,
-			unsigned long flags, unsigned long desc)
+static int __region_intersects(struct resource *parent, resource_size_t start,
+			       size_t size, unsigned long flags,
+			       unsigned long desc)
 {
 	struct resource res;
 	int type = 0; int other = 0;
@@ -499,7 +500,7 @@  static int __region_intersects(resource_size_t start, size_t size,
 	res.start = start;
 	res.end = start + size - 1;
 
-	for (p = iomem_resource.child; p ; p = p->sibling) {
+	for (p = parent->child; p ; p = p->sibling) {
 		bool is_type = (((p->flags & flags) == flags) &&
 				((desc == IORES_DESC_NONE) ||
 				 (desc == p->desc)));
@@ -543,7 +544,7 @@  int region_intersects(resource_size_t start, size_t size, unsigned long flags,
 	int ret;
 
 	read_lock(&resource_lock);
-	ret = __region_intersects(start, size, flags, desc);
+	ret = __region_intersects(&iomem_resource, start, size, flags, desc);
 	read_unlock(&resource_lock);
 
 	return ret;
@@ -1780,62 +1781,135 @@  void resource_list_free(struct list_head *head)
 }
 EXPORT_SYMBOL(resource_list_free);
 
-#ifdef CONFIG_DEVICE_PRIVATE
-static struct resource *__request_free_mem_region(struct device *dev,
-		struct resource *base, unsigned long size, const char *name)
+#ifdef CONFIG_GET_FREE_REGION
+#define GFR_DESCENDING		(1UL << 0)
+#define GFR_REQUEST_REGION	(1UL << 1)
+#define GFR_DEFAULT_ALIGN (1UL << PA_SECTION_SHIFT)
+
+static resource_size_t gfr_start(struct resource *base, resource_size_t size,
+				 resource_size_t align, unsigned long flags)
+{
+	if (flags & GFR_DESCENDING) {
+		resource_size_t end;
+
+		end = min_t(resource_size_t, base->end,
+			    (1ULL << MAX_PHYSMEM_BITS) - 1);
+		return end - size + 1;
+	}
+
+	return ALIGN(base->start, align);
+}
+
+static bool gfr_continue(struct resource *base, resource_size_t addr,
+			 resource_size_t size, unsigned long flags)
+{
+	if (flags & GFR_DESCENDING)
+		return addr > size && addr >= base->start;
+	return addr > addr - size &&
+	       addr <= min_t(resource_size_t, base->end,
+			     (1ULL << MAX_PHYSMEM_BITS) - 1);
+}
+
+static resource_size_t gfr_next(resource_size_t addr, resource_size_t size,
+				unsigned long flags)
+{
+	if (flags & GFR_DESCENDING)
+		return addr - size;
+	return addr + size;
+}
+
+static void remove_free_mem_region(void *_res)
 {
-	resource_size_t end, addr;
+	struct resource *res = _res;
+
+	if (res->parent)
+		remove_resource(res);
+	free_resource(res);
+}
+
+static struct resource *
+get_free_mem_region(struct device *dev, struct resource *base,
+		    resource_size_t size, const unsigned long align,
+		    const char *name, const unsigned long desc,
+		    const unsigned long flags)
+{
+	resource_size_t addr;
 	struct resource *res;
 	struct region_devres *dr = NULL;
 
-	size = ALIGN(size, 1UL << PA_SECTION_SHIFT);
-	end = min_t(unsigned long, base->end, (1UL << MAX_PHYSMEM_BITS) - 1);
-	addr = end - size + 1UL;
+	size = ALIGN(size, align);
 
 	res = alloc_resource(GFP_KERNEL);
 	if (!res)
 		return ERR_PTR(-ENOMEM);
 
-	if (dev) {
+	if (dev && (flags & GFR_REQUEST_REGION)) {
 		dr = devres_alloc(devm_region_release,
 				sizeof(struct region_devres), GFP_KERNEL);
 		if (!dr) {
 			free_resource(res);
 			return ERR_PTR(-ENOMEM);
 		}
+	} else if (dev) {
+		if (devm_add_action_or_reset(dev, remove_free_mem_region, res))
+			return ERR_PTR(-ENOMEM);
 	}
 
 	write_lock(&resource_lock);
-	for (; addr > size && addr >= base->start; addr -= size) {
-		if (__region_intersects(addr, size, 0, IORES_DESC_NONE) !=
-				REGION_DISJOINT)
+	for (addr = gfr_start(base, size, align, flags);
+	     gfr_continue(base, addr, size, flags);
+	     addr = gfr_next(addr, size, flags)) {
+		if (__region_intersects(base, addr, size, 0, IORES_DESC_NONE) !=
+		    REGION_DISJOINT)
 			continue;
 
-		if (__request_region_locked(res, &iomem_resource, addr, size,
-						name, 0))
-			break;
+		if (flags & GFR_REQUEST_REGION) {
+			if (__request_region_locked(res, &iomem_resource, addr,
+						    size, name, 0))
+				break;
 
-		if (dev) {
-			dr->parent = &iomem_resource;
-			dr->start = addr;
-			dr->n = size;
-			devres_add(dev, dr);
-		}
+			if (dev) {
+				dr->parent = &iomem_resource;
+				dr->start = addr;
+				dr->n = size;
+				devres_add(dev, dr);
+			}
 
-		res->desc = IORES_DESC_DEVICE_PRIVATE_MEMORY;
-		write_unlock(&resource_lock);
+			res->desc = desc;
+			write_unlock(&resource_lock);
+
+
+			/*
+			 * A driver is claiming this region so revoke any
+			 * mappings.
+			 */
+			revoke_iomem(res);
+		} else {
+			res->start = addr;
+			res->end = addr + size - 1;
+			res->name = name;
+			res->desc = desc;
+			res->flags = IORESOURCE_MEM;
+
+			/*
+			 * Only succeed if the resource hosts an exclusive
+			 * range after the insert
+			 */
+			if (__insert_resource(base, res) || res->child)
+				break;
+
+			write_unlock(&resource_lock);
+		}
 
-		/*
-		 * A driver is claiming this region so revoke any mappings.
-		 */
-		revoke_iomem(res);
 		return res;
 	}
 	write_unlock(&resource_lock);
 
-	free_resource(res);
-	if (dr)
+	if (flags & GFR_REQUEST_REGION) {
+		free_resource(res);
 		devres_free(dr);
+	} else if (dev)
+		devm_release_action(dev, remove_free_mem_region, res);
 
 	return ERR_PTR(-ERANGE);
 }
@@ -1854,18 +1928,48 @@  static struct resource *__request_free_mem_region(struct device *dev,
 struct resource *devm_request_free_mem_region(struct device *dev,
 		struct resource *base, unsigned long size)
 {
-	return __request_free_mem_region(dev, base, size, dev_name(dev));
+	unsigned long flags = GFR_DESCENDING | GFR_REQUEST_REGION;
+
+	return get_free_mem_region(dev, base, size, GFR_DEFAULT_ALIGN,
+				   dev_name(dev),
+				   IORES_DESC_DEVICE_PRIVATE_MEMORY, flags);
 }
 EXPORT_SYMBOL_GPL(devm_request_free_mem_region);
 
 struct resource *request_free_mem_region(struct resource *base,
 		unsigned long size, const char *name)
 {
-	return __request_free_mem_region(NULL, base, size, name);
+	unsigned long flags = GFR_DESCENDING | GFR_REQUEST_REGION;
+
+	return get_free_mem_region(NULL, base, size, GFR_DEFAULT_ALIGN, name,
+				   IORES_DESC_DEVICE_PRIVATE_MEMORY, flags);
 }
 EXPORT_SYMBOL_GPL(request_free_mem_region);
 
-#endif /* CONFIG_DEVICE_PRIVATE */
+/**
+ * alloc_free_mem_region - find a free region relative to @base
+ * @base: resource that will parent the new resource
+ * @size: size in bytes of memory to allocate from @base
+ * @align: alignment requirements for the allocation
+ * @name: resource name
+ *
+ * Buses like CXL, that can dynamically instantiate new memory regions,
+ * need a method to allocate physical address space for those regions.
+ * Allocate and insert a new resource to cover a free, unclaimed by a
+ * descendant of @base, range in the span of @base.
+ */
+struct resource *alloc_free_mem_region(struct resource *base,
+				       unsigned long size, unsigned long align,
+				       const char *name)
+{
+	/* GFR_ASCENDING | GFR_INSERT_RESOURCE */
+	unsigned long flags = 0;
+
+	return get_free_mem_region(NULL, base, size, align, name,
+				   IORES_DESC_NONE, flags);
+}
+EXPORT_SYMBOL_NS_GPL(alloc_free_mem_region, CXL);
+#endif /* CONFIG_GET_FREE_REGION */
 
 static int __init strict_iomem(char *str)
 {
diff --git a/mm/Kconfig b/mm/Kconfig
index 169e64192e48..a5b4fee2e3fd 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -994,9 +994,14 @@  config HMM_MIRROR
 	bool
 	depends on MMU
 
+config GET_FREE_REGION
+	depends on SPARSEMEM
+	bool
+
 config DEVICE_PRIVATE
 	bool "Unaddressable device memory (GPU memory, ...)"
 	depends on ZONE_DEVICE
+	select GET_FREE_REGION
 
 	help
 	  Allows creation of struct pages to represent unaddressable device