Commit 1b3f2bd0 authored by Dan Williams's avatar Dan Williams Committed by Dave Hansen
Browse files

x86/devmem: Remove duplicate range_is_allowed() definition 



17 years ago, Venki suggested [1] "A future improvement would be to
avoid the range_is_allowed duplication".

The only thing preventing a common implementation is that
phys_mem_access_prot_allowed() expects the range check to exit
immediately when PAT is disabled [2]. I.e. there is no cache conflict to
manage in that case. This cleanup was noticed on the path to
considering changing range_is_allowed() policy to blanket deny /dev/mem
for private (confidential computing) memory.

Note, however that phys_mem_access_prot_allowed() has long since stopped
being relevant for managing cache-type validation due to [3], and [4].

Commit 0124cecf ("x86, PAT: disable /dev/mem mmap RAM with PAT") [1]
Commit 9e41bff2 ("x86: fix /dev/mem mmap breakage when PAT is disabled") [2]
Commit 1886297c ("x86/mm/pat: Fix BUG_ON() in mmap_mem() on QEMU/i386") [3]
Commit 0c3c8a18 ("x86, PAT: Remove duplicate memtype reserve in devmem mmap") [4]

Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: default avatarNikolay Borisov <nik.borisov@suse.com>
Reviewed-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/all/20250430024622.1134277-2-dan.j.williams%40intel.com
parent eaa607de

arch/x86/mm/pat/memtype.c

+4 −27
Original line number Diff line number Diff line
@@ -38,6 +38,7 @@ 
#include <linux/kernel.h>

#include <linux/pfn_t.h>

#include <linux/slab.h>

#include <linux/io.h>

#include <linux/mm.h>

#include <linux/highmem.h>

#include <linux/fs.h>
@@ -773,38 +774,14 @@ pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn, 
	return vma_prot;

}



#ifdef CONFIG_STRICT_DEVMEM

/* This check is done in drivers/char/mem.c in case of STRICT_DEVMEM */

static inline int range_is_allowed(unsigned long pfn, unsigned long size)

{

	return 1;

}

#else

/* This check is needed to avoid cache aliasing when PAT is enabled */

static inline int range_is_allowed(unsigned long pfn, unsigned long size)

{

	u64 from = ((u64)pfn) << PAGE_SHIFT;

	u64 to = from + size;

	u64 cursor = from;



	if (!pat_enabled())

		return 1;



	while (cursor < to) {

		if (!devmem_is_allowed(pfn))

			return 0;

		cursor += PAGE_SIZE;

		pfn++;

	}

	return 1;

}

#endif /* CONFIG_STRICT_DEVMEM */



int phys_mem_access_prot_allowed(struct file *file, unsigned long pfn,

				unsigned long size, pgprot_t *vma_prot)

{

	enum page_cache_mode pcm = _PAGE_CACHE_MODE_WB;



	if (!pat_enabled())

		return 1;



	if (!range_is_allowed(pfn, size))

		return 0;

drivers/char/mem.c

+0 −18
Original line number Diff line number Diff line
@@ -61,29 +61,11 @@ static inline int page_is_allowed(unsigned long pfn) 
{

	return devmem_is_allowed(pfn);

}

static inline int range_is_allowed(unsigned long pfn, unsigned long size)

{

	u64 from = ((u64)pfn) << PAGE_SHIFT;

	u64 to = from + size;

	u64 cursor = from;



	while (cursor < to) {

		if (!devmem_is_allowed(pfn))

			return 0;

		cursor += PAGE_SIZE;

		pfn++;

	}

	return 1;

}

#else

static inline int page_is_allowed(unsigned long pfn)

{

	return 1;

}

static inline int range_is_allowed(unsigned long pfn, unsigned long size)

{

	return 1;

}

#endif



static inline bool should_stop_iteration(void)

include/linux/io.h

+21 −0
Original line number Diff line number Diff line
@@ -183,4 +183,25 @@ static inline void arch_io_free_memtype_wc(resource_size_t base, 
int devm_arch_io_reserve_memtype_wc(struct device *dev, resource_size_t start,

				    resource_size_t size);



#ifdef CONFIG_STRICT_DEVMEM

static inline int range_is_allowed(unsigned long pfn, unsigned long size)

{

	u64 from = ((u64)pfn) << PAGE_SHIFT;

	u64 to = from + size;

	u64 cursor = from;



	while (cursor < to) {

		if (!devmem_is_allowed(pfn))

			return 0;

		cursor += PAGE_SIZE;

		pfn++;

	}

	return 1;

}

#else

static inline int range_is_allowed(unsigned long pfn, unsigned long size)

{

	return 1;

}

#endif

#endif /* _LINUX_IO_H */