diff options
Diffstat (limited to 'Documentation/ia64/aliasing.txt')
| -rw-r--r-- | Documentation/ia64/aliasing.txt | 71 |
1 files changed, 37 insertions, 34 deletions
diff --git a/Documentation/ia64/aliasing.txt b/Documentation/ia64/aliasing.txt index 38f9a52..9a431a7 100644 --- a/Documentation/ia64/aliasing.txt +++ b/Documentation/ia64/aliasing.txt @@ -112,16 +112,6 @@ POTENTIAL ATTRIBUTE ALIASING CASES 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 @@ -138,14 +128,20 @@ POTENTIAL ATTRIBUTE ALIASING CASES ioremap() - This returns a kernel identity mapping for use inside the - kernel. + This returns a 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. + specified there. + + 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). + + If the granule contains non-WB memory, but we can cover the + region safely with kernel page table mappings, we can use + ioremap_page_range() as most other architectures do. + + Failing all of the above, we have to fall back to a UC mapping. PAST PROBLEM CASES @@ -158,7 +154,7 @@ PAST PROBLEM CASES 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 + mmap of 0x0-0x9FFFF /dev/mem by "hwinfo" on HP sx1000 with VGA enabled See https://bugzilla.novell.com/show_bug.cgi?id=140858. @@ -171,28 +167,25 @@ PAST PROBLEM CASES 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. + which uses a granule-sized UC mapping. This granule will cover 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. + If the EFI memory map reports that the entire range supports the + same attributes, we can allow the mmap (and we will prefer WB if + supported, as is the case with HP sx[12]000 machines with VGA + disabled). - 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. + If EFI reports the range as partly WB and partly UC (as on sx[12]000 + machines with VGA enabled), we must fail the mmap because there's no + safe attribute to use. - 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. + If EFI reports some of the range but not all (as on Intel firmware + that doesn't report the VGA frame buffer at all), we should fail the + mmap and force the user to map just the specific region of interest. mmap of 0xA0000-0xBFFFF legacy_mem by "X" on HP sx1000 with VGA disabled @@ -202,6 +195,16 @@ PAST PROBLEM CASES This is a special case of the previous case, and the mmap should fail for the same reason as above. + read of /sys/devices/.../rom + + For VGA devices, this may cause an ioremap() of 0xC0000. This + used to be done with a UC mapping, because the VGA frame buffer + at 0xA0000 prevents use of a WB granule. The UC mapping causes + an MCA on HP sx[12]000 chipsets. + + We should use WB page table mappings to avoid covering the VGA + frame buffer. + NOTES [1] SDM rev 2.2, vol 2, sec 4.4.1. |
