resource: Introduce alloc_free_mem_region()

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()).

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.

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@lst.de>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/165784333333.1758207.13703329337805274043.stgit@dwillia2-xfh.jf.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

diff --git a/include/linux/ioport.h b/include/linux/ioport.h
index 79d1ad6..616b683 100644 (file)
--- a/include/linux/ioport.h
+++ b/include/linux/ioport.h
@@ -330,6 +330,8 @@ 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 53a534d..4c5e80b 100644 (file)
--- 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 +1781,139 @@ 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;
+       /*
+        * In the ascend case be careful that the last increment by
+        * @size did not wrap 0.
+        */
+       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)
+{
+       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 end, addr;
+       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 +1932,48 @@ 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)
+{
+       /* 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 169e641..a5b4fee 100644 (file)
--- 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