x86: fix Xorg crash with xf86MapVidMem error (282c454c) · Commits · 戴 / test

Clarify the usage of mtrr_lookup() in PAT code, and to make PAT code resilient to mtrr lookup problems. Specifically, pat_x_mtrr_type() is restructured to highlight, under what conditions we look for mtrr hint. pat_x_mtrr_type() uses a default type when there are any errors in mtrr lookup (still maintaining the pat consistency). And, reserve_memtype() highlights its usage ot mtrr_lookup for request type of '-1' and also defaults in a sane way on any mtrr lookup failure. pat.c looks at mtrr type of a range to get a hint on what mapping type to request when user/API: (1) hasn't specified any type (/dev/mem mapping) and we do not want to take performance hit by always mapping UC_MINUS. This will be the case for /dev/mem mappings used to map BIOS area or ACPI region which are WB'able. In this case, as long as MTRR is not WB, PAT will request UC_MINUS for such mappings. (2) user/API requests WB mapping while in reality MTRR may have UC or WC. In this case, PAT can map as WB (without checking MTRR) and still effective type will be UC or WC. But, a subsequent request to map same region as UC or WC may fail, as the region will get trackked as WB in PAT list. Looking at MTRR hint helps us to track based on effective type rather than what user requested. Again, here mtrr_lookup is only used as hint and we fallback to WB mapping (as requested by user) as default. In both cases, after using the mtrr hint, we still go through the memtype list to make sure there are no inconsistencies among multiple users. Signed-off-by:

Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> Signed-off-by:

Suresh Siddha <suresh.b.siddha@intel.com> Tested-by:

Rufus & Azrael <rufus-azrael@numericable.fr> Signed-off-by:

Ingo Molnar <mingo@elte.hu>

arch/x86/mm/pat.c

+24 −25

Original line number	Diff line number	Diff line
		@@ -151,32 +151,33 @@ static int pat_x_mtrr_type(u64 start, u64 end, unsigned long prot,
		unsigned long pat_type;
		u8 mtrr_type;

		mtrr_type = mtrr_type_lookup(start, end);
		if (mtrr_type == 0xFF) { /* MTRR not enabled */
		*ret_prot = prot;
		return 0;
		}
		if (mtrr_type == 0xFE) { /* MTRR match error */
		*ret_prot = _PAGE_CACHE_UC;
		return -1;
		}
		if (mtrr_type != MTRR_TYPE_UNCACHABLE &&
		mtrr_type != MTRR_TYPE_WRBACK &&
		mtrr_type != MTRR_TYPE_WRCOMB) { /* MTRR type unhandled */
		*ret_prot = _PAGE_CACHE_UC;
		return -1;
		}

		pat_type = prot & _PAGE_CACHE_MASK;
		prot &= (~_PAGE_CACHE_MASK);

		/* Currently doing intersection by hand. Optimize it later. */
		/*
		* We return the PAT request directly for types where PAT takes
		* precedence with respect to MTRR and for UC_MINUS.
		* Consistency checks with other PAT requests is done later
		* while going through memtype list.
		*/
		if (pat_type == _PAGE_CACHE_WC) {
		*ret_prot = prot \| _PAGE_CACHE_WC;
		return 0;
		} else if (pat_type == _PAGE_CACHE_UC_MINUS) {
		*ret_prot = prot \| _PAGE_CACHE_UC_MINUS;
		} else if (pat_type == _PAGE_CACHE_UC \|\|
		mtrr_type == MTRR_TYPE_UNCACHABLE) {
		return 0;
		} else if (pat_type == _PAGE_CACHE_UC) {
		*ret_prot = prot \| _PAGE_CACHE_UC;
		return 0;
		}

		/*
		* Look for MTRR hint to get the effective type in case where PAT
		* request is for WB.
		*/
		mtrr_type = mtrr_type_lookup(start, end);

		if (mtrr_type == MTRR_TYPE_UNCACHABLE) {
		*ret_prot = prot \| _PAGE_CACHE_UC;
		} else if (mtrr_type == MTRR_TYPE_WRCOMB) {
		*ret_prot = prot \| _PAGE_CACHE_WC;
		@@ -233,14 +234,12 @@ int reserve_memtype(u64 start, u64 end, unsigned long req_type,

		if (req_type == -1) {
		/*
		* Special case where caller wants to inherit from mtrr or
		* existing pat mapping, defaulting to UC_MINUS in case of
		* no match.
		* Call mtrr_lookup to get the type hint. This is an
		* optimization for /dev/mem mmap'ers into WB memory (BIOS
		* tools and ACPI tools). Use WB request for WB memory and use
		* UC_MINUS otherwise.
		*/
		u8 mtrr_type = mtrr_type_lookup(start, end);
		if (mtrr_type == 0xFE) { /* MTRR match error */
		err = -1;
		}

		if (mtrr_type == MTRR_TYPE_WRBACK) {
		req_type = _PAGE_CACHE_WB;

Admin message