We currently attempt to check whether a physical address range provided to __ioremap() may be in use by the page allocator by examining the value of PageReserved for each page in the region - lowmem pages not marked reserved are presumed to be in use by the page allocator, and requests to ioremap them fail.
The way we check this has been broken since commit 92923ca3aace ("mm: meminit: only set page reserved in the memblock region"), because memblock will typically not have any knowledge of non-RAM pages and therefore those pages will not have the PageReserved flag set. Thus when we attempt to ioremap a region outside of RAM we incorrectly fail believing that the region is RAM that may be in use.
In most cases ioremap() on MIPS will take a fast-path to use the unmapped kseg1 or xkphys virtual address spaces and never hit this path, so the only way to hit it is for a MIPS32 system to attempt to ioremap() an address range in lowmem with flags other than _CACHE_UNCACHED. Perhaps the most straightforward way to do this is using ioremap_uncached_accelerated(), which is how the problem was discovered.
Fix this by making use of walk_system_ram_range() to test the address range provided to __ioremap() against only RAM pages, rather than all lowmem pages. This means that if we have a lowmem I/O region, which is very common for MIPS systems, we're free to ioremap() address ranges within it. A nice bonus is that the test is no longer limited to lowmem.
The approach here matches the way x86 performed the same test after commit c81c8a1eeede ("x86, ioremap: Speed up check for RAM pages") until x86 moved towards a slightly more complicated check using walk_mem_res() for unrelated reasons with commit 0e4c12b45aa8 ("x86/mm, resource: Use PAGE_KERNEL protection for ioremap of memory pages").
Signed-off-by: Paul Burton paul.burton@mips.com Reported-by: Serge Semin fancer.lancer@gmail.com Tested-by: Serge Semin fancer.lancer@gmail.com Fixes: 92923ca3aace ("mm: meminit: only set page reserved in the memblock region") Cc: James Hogan jhogan@kernel.org Cc: Ralf Baechle ralf@linux-mips.org Cc: linux-mips@linux-mips.org Cc: stable@vger.kernel.org # v4.2+
---
arch/mips/mm/ioremap.c | 37 +++++++++++++++++++++++++------------ 1 file changed, 25 insertions(+), 12 deletions(-)
diff --git a/arch/mips/mm/ioremap.c b/arch/mips/mm/ioremap.c index 1986e09fb457..1601d90b087b 100644 --- a/arch/mips/mm/ioremap.c +++ b/arch/mips/mm/ioremap.c @@ -9,6 +9,7 @@ #include <linux/export.h> #include <asm/addrspace.h> #include <asm/byteorder.h> +#include <linux/ioport.h> #include <linux/sched.h> #include <linux/slab.h> #include <linux/vmalloc.h> @@ -98,6 +99,20 @@ static int remap_area_pages(unsigned long address, phys_addr_t phys_addr, return error; }
+static int __ioremap_check_ram(unsigned long start_pfn, unsigned long nr_pages, + void *arg) +{ + unsigned long i; + + for (i = 0; i < nr_pages; i++) { + if (pfn_valid(start_pfn + i) && + !PageReserved(pfn_to_page(start_pfn + i))) + return 1; + } + + return 0; +} + /* * Generic mapping function (not visible outside): */ @@ -116,8 +131,8 @@ static int remap_area_pages(unsigned long address, phys_addr_t phys_addr,
void __iomem * __ioremap(phys_addr_t phys_addr, phys_addr_t size, unsigned long flags) { + unsigned long offset, pfn, last_pfn; struct vm_struct * area; - unsigned long offset; phys_addr_t last_addr; void * addr;
@@ -137,18 +152,16 @@ void __iomem * __ioremap(phys_addr_t phys_addr, phys_addr_t size, unsigned long return (void __iomem *) CKSEG1ADDR(phys_addr);
/* - * Don't allow anybody to remap normal RAM that we're using.. + * Don't allow anybody to remap RAM that may be allocated by the page + * allocator, since that could lead to races & data clobbering. */ - if (phys_addr < virt_to_phys(high_memory)) { - char *t_addr, *t_end; - struct page *page; - - t_addr = __va(phys_addr); - t_end = t_addr + (size - 1); - - for(page = virt_to_page(t_addr); page <= virt_to_page(t_end); page++) - if(!PageReserved(page)) - return NULL; + pfn = PFN_DOWN(phys_addr); + last_pfn = PFN_DOWN(last_addr); + if (walk_system_ram_range(pfn, last_pfn - pfn + 1, NULL, + __ioremap_check_ram) == 1) { + WARN_ONCE(1, "ioremap on RAM at %pa - %pa\n", + &phys_addr, &last_addr); + return NULL; }
/*