--- /dev/null
+ MEMORY ATTRIBUTE ALIASING ON IA-64
+
+ Bjorn Helgaas
+ <bjorn.helgaas@hp.com>
+ May 4, 2006
+
+
+MEMORY ATTRIBUTES
+
+ Itanium supports several attributes for virtual memory references.
+ The attribute is part of the virtual translation, i.e., it is
+ contained in the TLB entry. The ones of most interest to the Linux
+ kernel are:
+
+ WB Write-back (cacheable)
+ UC Uncacheable
+ WC Write-coalescing
+
+ System memory typically uses the WB attribute. The UC attribute is
+ used for memory-mapped I/O devices. The WC attribute is uncacheable
+ like UC is, but writes may be delayed and combined to increase
+ performance for things like frame buffers.
+
+ The Itanium architecture requires that we avoid accessing the same
+ page with both a cacheable mapping and an uncacheable mapping[1].
+
+ The design of the chipset determines which attributes are supported
+ on which regions of the address space. For example, some chipsets
+ support either WB or UC access to main memory, while others support
+ only WB access.
+
+MEMORY MAP
+
+ Platform firmware describes the physical memory map and the
+ supported attributes for each region. At boot-time, the kernel uses
+ the EFI GetMemoryMap() interface. ACPI can also describe memory
+ devices and the attributes they support, but Linux/ia64 currently
+ doesn't use this information.
+
+ The kernel uses the efi_memmap table returned from GetMemoryMap() to
+ learn the attributes supported by each region of physical address
+ space. Unfortunately, this table does not completely describe the
+ address space because some machines omit some or all of the MMIO
+ regions from the map.
+
+ The kernel maintains another table, kern_memmap, which describes the
+ memory Linux is actually using and the attribute for each region.
+ This contains only system memory; it does not contain MMIO space.
+
+ The kern_memmap table typically contains only a subset of the system
+ memory described by the efi_memmap. Linux/ia64 can't use all memory
+ in the system because of constraints imposed by the identity mapping
+ scheme.
+
+ The efi_memmap table is preserved unmodified because the original
+ boot-time information is required for kexec.
+
+KERNEL IDENTITY MAPPINGS
+
+ Linux/ia64 identity mappings are done with large pages, currently
+ either 16MB or 64MB, referred to as "granules." Cacheable mappings
+ are speculative[2], so the processor can read any location in the
+ page at any time, independent of the programmer's intentions. This
+ means that to avoid attribute aliasing, Linux can create a cacheable
+ identity mapping only when the entire granule supports cacheable
+ access.
+
+ Therefore, kern_memmap contains only full granule-sized regions that
+ can referenced safely by an identity mapping.
+
+ Uncacheable mappings are not speculative, so the processor will
+ generate UC accesses only to locations explicitly referenced by
+ software. This allows UC identity mappings to cover granules that
+ are only partially populated, or populated with a combination of UC
+ and WB regions.
+
+USER MAPPINGS
+
+ User mappings are typically done with 16K or 64K pages. The smaller
+ page size allows more flexibility because only 16K or 64K has to be
+ homogeneous with respect to memory attributes.
+
+POTENTIAL ATTRIBUTE ALIASING CASES
+
+ There are several ways the kernel creates new mappings:
+
+ mmap of /dev/mem
+
+ This uses remap_pfn_range(), which creates user mappings. These
+ mappings may be either WB or UC. If the region being mapped
+ happens to be in kern_memmap, meaning that it may also be mapped
+ by a kernel identity mapping, the user mapping must use the same
+ attribute as the kernel mapping.
+
+ If the region is not in kern_memmap, the user mapping should use
+ an attribute reported as being supported in the EFI memory map.
+
+ Since the EFI memory map does not describe MMIO on some
+ machines, this should use an uncacheable mapping as a fallback.
+
+ mmap of /sys/class/pci_bus/.../legacy_mem
+
+ This is very similar to mmap of /dev/mem, except that legacy_mem
+ only allows mmap of the one megabyte "legacy MMIO" area for a
+ specific PCI bus. Typically this is the first megabyte of
+ physical address space, but it may be different on machines with
+ several VGA devices.
+
+ "X" uses this to access VGA frame buffers. Using legacy_mem
+ rather than /dev/mem allows multiple instances of X to talk to
+ different VGA cards.
+
+ The /dev/mem mmap constraints apply.
+
+ However, since this is for mapping legacy MMIO space, WB access
+ does not make sense. This matters on machines without legacy
+ VGA support: these machines may have WB memory for the entire
+ first megabyte (or even the entire first granule).
+
+ On these machines, we could mmap legacy_mem as WB, which would
+ be safe in terms of attribute aliasing, but X has no way of
+ knowing that it is accessing regular memory, not a frame buffer,
+ so the kernel should fail the mmap rather than doing it with WB.
+
+ read/write of /dev/mem
+
+ This uses copy_from_user(), which implicitly uses a kernel
+ identity mapping. This is obviously safe for things in
+ kern_memmap.
+
+ There may be corner cases of things that are not in kern_memmap,
+ but could be accessed this way. For example, registers in MMIO
+ space are not in kern_memmap, but could be accessed with a UC
+ mapping. This would not cause attribute aliasing. But
+ registers typically can be accessed only with four-byte or
+ eight-byte accesses, and the copy_from_user() path doesn't allow
+ any control over the access size, so this would be dangerous.
+
+ ioremap()
+
+ This returns a kernel identity mapping for use inside the
+ kernel.
+
+ If the region is in kern_memmap, we should use the attribute
+ specified there. Otherwise, if the EFI memory map reports that
+ the entire granule supports WB, we should use that (granules
+ that are partially reserved or occupied by firmware do not appear
+ in kern_memmap). Otherwise, we should use a UC mapping.
+
+PAST PROBLEM CASES
+
+ mmap of various MMIO regions from /dev/mem by "X" on Intel platforms
+
+ The EFI memory map may not report these MMIO regions.
+
+ These must be allowed so that X will work. This means that
+ when the EFI memory map is incomplete, every /dev/mem mmap must
+ succeed. It may create either WB or UC user mappings, depending
+ on whether the region is in kern_memmap or the EFI memory map.
+
+ mmap of 0x0-0xA0000 /dev/mem by "hwinfo" on HP sx1000 with VGA enabled
+
+ See https://bugzilla.novell.com/show_bug.cgi?id=140858.
+
+ The EFI memory map reports the following attributes:
+ 0x00000-0x9FFFF WB only
+ 0xA0000-0xBFFFF UC only (VGA frame buffer)
+ 0xC0000-0xFFFFF WB only
+
+ This mmap is done with user pages, not kernel identity mappings,
+ so it is safe to use WB mappings.
+
+ The kernel VGA driver may ioremap the VGA frame buffer at 0xA0000,
+ which will use a granule-sized UC mapping covering 0-0xFFFFF. This
+ granule covers some WB-only memory, but since UC is non-speculative,
+ the processor will never generate an uncacheable reference to the
+ WB-only areas unless the driver explicitly touches them.
+
+ mmap of 0x0-0xFFFFF legacy_mem by "X"
+
+ If the EFI memory map reports this entire range as WB, there
+ is no VGA MMIO hole, and the mmap should fail or be done with
+ a WB mapping.
+
+ There's no easy way for X to determine whether the 0xA0000-0xBFFFF
+ region is a frame buffer or just memory, so I think it's best to
+ just fail this mmap request rather than using a WB mapping. As
+ far as I know, there's no need to map legacy_mem with WB
+ mappings.
+
+ Otherwise, a UC mapping of the entire region is probably safe.
+ The VGA hole means the region will not be in kern_memmap. The
+ HP sx1000 chipset doesn't support UC access to the memory surrounding
+ the VGA hole, but X doesn't need that area anyway and should not
+ reference it.
+
+ mmap of 0xA0000-0xBFFFF legacy_mem by "X" on HP sx1000 with VGA disabled
+
+ The EFI memory map reports the following attributes:
+ 0x00000-0xFFFFF WB only (no VGA MMIO hole)
+
+ This is a special case of the previous case, and the mmap should
+ fail for the same reason as above.
+
+NOTES
+
+ [1] SDM rev 2.2, vol 2, sec 4.4.1.
+ [2] SDM rev 2.2, vol 2, sec 4.4.6.
* Copyright (C) 1999-2003 Hewlett-Packard Co.
* David Mosberger-Tang <davidm@hpl.hp.com>
* Stephane Eranian <eranian@hpl.hp.com>
+ * (c) Copyright 2006 Hewlett-Packard Development Company, L.P.
+ * Bjorn Helgaas <bjorn.helgaas@hp.com>
*
* All EFI Runtime Services are not implemented yet as EFI only
* supports physical mode addressing on SoftSDV. This is to be fixed
return 0;
}
-static efi_memory_desc_t *
-efi_memory_descriptor (unsigned long phys_addr)
+static struct kern_memdesc *
+kern_memory_descriptor (unsigned long phys_addr)
{
- void *efi_map_start, *efi_map_end, *p;
- efi_memory_desc_t *md;
- u64 efi_desc_size;
-
- efi_map_start = __va(ia64_boot_param->efi_memmap);
- efi_map_end = efi_map_start + ia64_boot_param->efi_memmap_size;
- efi_desc_size = ia64_boot_param->efi_memdesc_size;
+ struct kern_memdesc *md;
- for (p = efi_map_start; p < efi_map_end; p += efi_desc_size) {
- md = p;
-
- if (phys_addr - md->phys_addr < (md->num_pages << EFI_PAGE_SHIFT))
+ for (md = kern_memmap; md->start != ~0UL; md++) {
+ if (phys_addr - md->start < (md->num_pages << EFI_PAGE_SHIFT))
return md;
}
return 0;
}
-static int
-efi_memmap_has_mmio (void)
+static efi_memory_desc_t *
+efi_memory_descriptor (unsigned long phys_addr)
{
void *efi_map_start, *efi_map_end, *p;
efi_memory_desc_t *md;
for (p = efi_map_start; p < efi_map_end; p += efi_desc_size) {
md = p;
- if (md->type == EFI_MEMORY_MAPPED_IO)
- return 1;
+ if (phys_addr - md->phys_addr < (md->num_pages << EFI_PAGE_SHIFT))
+ return md;
}
return 0;
}
}
EXPORT_SYMBOL(efi_mem_attributes);
-/*
- * Determines whether the memory at phys_addr supports the desired
- * attribute (WB, UC, etc). If this returns 1, the caller can safely
- * access size bytes at phys_addr with the specified attribute.
- */
-int
-efi_mem_attribute_range (unsigned long phys_addr, unsigned long size, u64 attr)
+u64
+efi_mem_attribute (unsigned long phys_addr, unsigned long size)
{
unsigned long end = phys_addr + size;
efi_memory_desc_t *md = efi_memory_descriptor(phys_addr);
+ u64 attr;
+
+ if (!md)
+ return 0;
+
+ /*
+ * EFI_MEMORY_RUNTIME is not a memory attribute; it just tells
+ * the kernel that firmware needs this region mapped.
+ */
+ attr = md->attribute & ~EFI_MEMORY_RUNTIME;
+ do {
+ unsigned long md_end = efi_md_end(md);
+
+ if (end <= md_end)
+ return attr;
+
+ md = efi_memory_descriptor(md_end);
+ if (!md || (md->attribute & ~EFI_MEMORY_RUNTIME) != attr)
+ return 0;
+ } while (md);
+ return 0;
+}
+
+u64
+kern_mem_attribute (unsigned long phys_addr, unsigned long size)
+{
+ unsigned long end = phys_addr + size;
+ struct kern_memdesc *md;
+ u64 attr;
/*
- * Some firmware doesn't report MMIO regions in the EFI memory
- * map. The Intel BigSur (a.k.a. HP i2000) has this problem.
- * On those platforms, we have to assume UC is valid everywhere.
+ * This is a hack for ioremap calls before we set up kern_memmap.
+ * Maybe we should do efi_memmap_init() earlier instead.
*/
- if (!md || (md->attribute & attr) != attr) {
- if (attr == EFI_MEMORY_UC && !efi_memmap_has_mmio())
- return 1;
+ if (!kern_memmap) {
+ attr = efi_mem_attribute(phys_addr, size);
+ if (attr & EFI_MEMORY_WB)
+ return EFI_MEMORY_WB;
return 0;
}
+ md = kern_memory_descriptor(phys_addr);
+ if (!md)
+ return 0;
+
+ attr = md->attribute;
do {
- unsigned long md_end = efi_md_end(md);
+ unsigned long md_end = kmd_end(md);
if (end <= md_end)
- return 1;
+ return attr;
- md = efi_memory_descriptor(md_end);
- if (!md || (md->attribute & attr) != attr)
+ md = kern_memory_descriptor(md_end);
+ if (!md || md->attribute != attr)
return 0;
} while (md);
return 0;
}
+EXPORT_SYMBOL(kern_mem_attribute);
-/*
- * For /dev/mem, we only allow read & write system calls to access
- * write-back memory, because read & write don't allow the user to
- * control access size.
- */
int
valid_phys_addr_range (unsigned long phys_addr, unsigned long size)
{
- return efi_mem_attribute_range(phys_addr, size, EFI_MEMORY_WB);
+ u64 attr;
+
+ /*
+ * /dev/mem reads and writes use copy_to_user(), which implicitly
+ * uses a granule-sized kernel identity mapping. It's really
+ * only safe to do this for regions in kern_memmap. For more
+ * details, see Documentation/ia64/aliasing.txt.
+ */
+ attr = kern_mem_attribute(phys_addr, size);
+ if (attr & EFI_MEMORY_WB || attr & EFI_MEMORY_UC)
+ return 1;
+ return 0;
}
-/*
- * We allow mmap of anything in the EFI memory map that supports
- * either write-back or uncacheable access. For uncacheable regions,
- * the supported access sizes are system-dependent, and the user is
- * responsible for using the correct size.
- *
- * Note that this doesn't currently allow access to hot-added memory,
- * because that doesn't appear in the boot-time EFI memory map.
- */
int
valid_mmap_phys_addr_range (unsigned long phys_addr, unsigned long size)
{
- if (efi_mem_attribute_range(phys_addr, size, EFI_MEMORY_WB))
- return 1;
+ /*
+ * MMIO regions are often missing from the EFI memory map.
+ * We must allow mmap of them for programs like X, so we
+ * currently can't do any useful validation.
+ */
+ return 1;
+}
- if (efi_mem_attribute_range(phys_addr, size, EFI_MEMORY_UC))
- return 1;
+pgprot_t
+phys_mem_access_prot(struct file *file, unsigned long pfn, unsigned long size,
+ pgprot_t vma_prot)
+{
+ unsigned long phys_addr = pfn << PAGE_SHIFT;
+ u64 attr;
- return 0;
+ /*
+ * For /dev/mem mmap, we use user mappings, but if the region is
+ * in kern_memmap (and hence may be covered by a kernel mapping),
+ * we must use the same attribute as the kernel mapping.
+ */
+ attr = kern_mem_attribute(phys_addr, size);
+ if (attr & EFI_MEMORY_WB)
+ return pgprot_cacheable(vma_prot);
+ else if (attr & EFI_MEMORY_UC)
+ return pgprot_noncached(vma_prot);
+
+ /*
+ * Some chipsets don't support UC access to memory. If
+ * WB is supported, we prefer that.
+ */
+ if (efi_mem_attribute(phys_addr, size) & EFI_MEMORY_WB)
+ return pgprot_cacheable(vma_prot);
+
+ return pgprot_noncached(vma_prot);
}
int __init
#include <linux/module.h>
#include <linux/efi.h>
#include <asm/io.h>
+#include <asm/meminit.h>
static inline void __iomem *
__ioremap (unsigned long offset, unsigned long size)
void __iomem *
ioremap (unsigned long offset, unsigned long size)
{
- if (efi_mem_attribute_range(offset, size, EFI_MEMORY_WB))
- return phys_to_virt(offset);
+ u64 attr;
+ unsigned long gran_base, gran_size;
- if (efi_mem_attribute_range(offset, size, EFI_MEMORY_UC))
+ /*
+ * For things in kern_memmap, we must use the same attribute
+ * as the rest of the kernel. For more details, see
+ * Documentation/ia64/aliasing.txt.
+ */
+ attr = kern_mem_attribute(offset, size);
+ if (attr & EFI_MEMORY_WB)
+ return phys_to_virt(offset);
+ else if (attr & EFI_MEMORY_UC)
return __ioremap(offset, size);
/*
- * Someday this should check ACPI resources so we
- * can do the right thing for hot-plugged regions.
+ * Some chipsets don't support UC access to memory. If
+ * WB is supported for the whole granule, we prefer that.
*/
+ gran_base = GRANULEROUNDDOWN(offset);
+ gran_size = GRANULEROUNDUP(offset + size) - gran_base;
+ if (efi_mem_attribute(gran_base, gran_size) & EFI_MEMORY_WB)
+ return phys_to_virt(offset);
+
return __ioremap(offset, size);
}
EXPORT_SYMBOL(ioremap);
void __iomem *
ioremap_nocache (unsigned long offset, unsigned long size)
{
+ if (kern_mem_attribute(offset, size) & EFI_MEMORY_WB)
+ return 0;
+
return __ioremap(offset, size);
}
EXPORT_SYMBOL(ioremap_nocache);
int
pci_mmap_legacy_page_range(struct pci_bus *bus, struct vm_area_struct *vma)
{
+ unsigned long size = vma->vm_end - vma->vm_start;
+ pgprot_t prot;
char *addr;
+ /*
+ * Avoid attribute aliasing. See Documentation/ia64/aliasing.txt
+ * for more details.
+ */
+ if (!valid_mmap_phys_addr_range(vma->vm_pgoff << PAGE_SHIFT, size))
+ return -EINVAL;
+ prot = phys_mem_access_prot(NULL, vma->vm_pgoff, size,
+ vma->vm_page_prot);
+ if (pgprot_val(prot) != pgprot_val(pgprot_noncached(vma->vm_page_prot)))
+ return -EINVAL;
+
addr = pci_get_legacy_mem(bus);
if (IS_ERR(addr))
return PTR_ERR(addr);
vma->vm_pgoff += (unsigned long)addr >> PAGE_SHIFT;
- vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+ vma->vm_page_prot = prot;
vma->vm_flags |= (VM_SHM | VM_RESERVED | VM_IO);
if (remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff,
- vma->vm_end - vma->vm_start, vma->vm_page_prot))
+ size, vma->vm_page_prot))
return -EAGAIN;
return 0;
}
#define ARCH_HAS_VALID_PHYS_ADDR_RANGE
+extern u64 kern_mem_attribute (unsigned long phys_addr, unsigned long size);
extern int valid_phys_addr_range (unsigned long addr, size_t count); /* efi.c */
extern int valid_mmap_phys_addr_range (unsigned long addr, size_t count);
#define pte_mkhuge(pte) (__pte(pte_val(pte)))
/*
- * Macro to a page protection value as "uncacheable". Note that "protection" is really a
- * misnomer here as the protection value contains the memory attribute bits, dirty bits,
- * and various other bits as well.
+ * Make page protection values cacheable, uncacheable, or write-
+ * combining. Note that "protection" is really a misnomer here as the
+ * protection value contains the memory attribute bits, dirty bits, and
+ * various other bits as well.
*/
+#define pgprot_cacheable(prot) __pgprot((pgprot_val(prot) & ~_PAGE_MA_MASK) | _PAGE_MA_WB)
#define pgprot_noncached(prot) __pgprot((pgprot_val(prot) & ~_PAGE_MA_MASK) | _PAGE_MA_UC)
-
-/*
- * Macro to make mark a page protection value as "write-combining".
- * Note that "protection" is really a misnomer here as the protection
- * value contains the memory attribute bits, dirty bits, and various
- * other bits as well. Accesses through a write-combining translation
- * works bypasses the caches, but does allow for consecutive writes to
- * be combined into single (but larger) write transactions.
- */
#define pgprot_writecombine(prot) __pgprot((pgprot_val(prot) & ~_PAGE_MA_MASK) | _PAGE_MA_WC)
+struct file;
+extern pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
+ unsigned long size, pgprot_t vma_prot);
+#define __HAVE_PHYS_MEM_ACCESS_PROT
+
static inline unsigned long
pgd_index (unsigned long address)
{
extern u64 efi_get_iobase (void);
extern u32 efi_mem_type (unsigned long phys_addr);
extern u64 efi_mem_attributes (unsigned long phys_addr);
+extern u64 efi_mem_attribute (unsigned long phys_addr, unsigned long size);
extern int efi_mem_attribute_range (unsigned long phys_addr, unsigned long size,
u64 attr);
extern int __init efi_uart_console_only (void);
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