kernel/linux.git/arch/mips/mm, branch v4.9.331

MIPS: tlbex: Explicitly compare _PAGE_NO_EXEC against 0

2022-08-25T09:09:32+00:00

[ Upstream commit 74de14fe05dd6b151d73cb0c73c8ec874cbdcde6 ] When CONFIG_XPA is enabled, Clang warns: arch/mips/mm/tlbex.c:629:24: error: converting the result of '<<' to a boolean; did you mean '(1 << _PAGE_NO_EXEC_SHIFT) != 0'? [-Werror,-Wint-in-bool-context] if (cpu_has_rixi && !!_PAGE_NO_EXEC) { ^ arch/mips/include/asm/pgtable-bits.h:174:28: note: expanded from macro '_PAGE_NO_EXEC' # define _PAGE_NO_EXEC (1 << _PAGE_NO_EXEC_SHIFT) ^ arch/mips/mm/tlbex.c:2568:24: error: converting the result of '<<' to a boolean; did you mean '(1 << _PAGE_NO_EXEC_SHIFT) != 0'? [-Werror,-Wint-in-bool-context] if (!cpu_has_rixi || !_PAGE_NO_EXEC) { ^ arch/mips/include/asm/pgtable-bits.h:174:28: note: expanded from macro '_PAGE_NO_EXEC' # define _PAGE_NO_EXEC (1 << _PAGE_NO_EXEC_SHIFT) ^ 2 errors generated. _PAGE_NO_EXEC can be '0' or '1 << _PAGE_NO_EXEC_SHIFT' depending on the build and runtime configuration, which is what the negation operators are trying to convey. To silence the warning, explicitly compare against 0 so the result of the '<<' operator is not implicitly converted to a boolean. According to its documentation, GCC enables -Wint-in-bool-context with -Wall but this warning is not visible when building the same configuration with GCC. It appears GCC only warns when compiling C++, not C, although the documentation makes no note of this: https://godbolt.org/z/x39q3brxf Reported-by: Sudip Mukherjee (Codethink) Signed-off-by: Nathan Chancellor Signed-off-by: Thomas Bogendoerfer Signed-off-by: Sasha Levin

gup: document and work around "COW can break either way" issue

2022-01-27T07:47:42+00:00

commit 9bbd42e79720122334226afad9ddcac1c3e6d373 upstream. Doing a "get_user_pages()" on a copy-on-write page for reading can be ambiguous: the page can be COW'ed at any time afterwards, and the direction of a COW event isn't defined. Yes, whoever writes to it will generally do the COW, but if the thread that did the get_user_pages() unmapped the page before the write (and that could happen due to memory pressure in addition to any outright action), the writer could also just take over the old page instead. End result: the get_user_pages() call might result in a page pointer that is no longer associated with the original VM, and is associated with - and controlled by - another VM having taken it over instead. So when doing a get_user_pages() on a COW mapping, the only really safe thing to do would be to break the COW when getting the page, even when only getting it for reading. At the same time, some users simply don't even care. For example, the perf code wants to look up the page not because it cares about the page, but because the code simply wants to look up the physical address of the access for informational purposes, and doesn't really care about races when a page might be unmapped and remapped elsewhere. This adds logic to force a COW event by setting FOLL_WRITE on any copy-on-write mapping when FOLL_GET (or FOLL_PIN) is used to get a page pointer as a result. The current semantics end up being: - __get_user_pages_fast(): no change. If you don't ask for a write, you won't break COW. You'd better know what you're doing. - get_user_pages_fast(): the fast-case "look it up in the page tables without anything getting mmap_sem" now refuses to follow a read-only page, since it might need COW breaking. Which happens in the slow path - the fast path doesn't know if the memory might be COW or not. - get_user_pages() (including the slow-path fallback for gup_fast()): for a COW mapping, turn on FOLL_WRITE for FOLL_GET/FOLL_PIN, with very similar semantics to FOLL_FORCE. If it turns out that we want finer granularity (ie "only break COW when it might actually matter" - things like the zero page are special and don't need to be broken) we might need to push these semantics deeper into the lookup fault path. So if people care enough, it's possible that we might end up adding a new internal FOLL_BREAK_COW flag to go with the internal FOLL_COW flag we already have for tracking "I had a COW". Alternatively, if it turns out that different callers might want to explicitly control the forced COW break behavior, we might even want to make such a flag visible to the users of get_user_pages() instead of using the above default semantics. But for now, this is mostly commentary on the issue (this commit message being a lot bigger than the patch, and that patch in turn is almost all comments), with that minimal "enable COW breaking early" logic using the existing FOLL_WRITE behavior. [ It might be worth noting that we've always had this ambiguity, and it could arguably be seen as a user-space issue. You only get private COW mappings that could break either way in situations where user space is doing cooperative things (ie fork() before an execve() etc), but it _is_ surprising and very subtle, and fork() is supposed to give you independent address spaces. So let's treat this as a kernel issue and make the semantics of get_user_pages() easier to understand. Note that obviously a true shared mapping will still get a page that can change under us, so this does _not_ mean that get_user_pages() somehow returns any "stable" page ] [surenb: backport notes Replaced (gup_flags | FOLL_WRITE) with write=1 in gup_pgd_range. Removed FOLL_PIN usage in should_force_cow_break since it's missing in the earlier kernels.] Reported-by: Jann Horn Tested-by: Christoph Hellwig Acked-by: Oleg Nesterov Acked-by: Kirill Shutemov Acked-by: Jan Kara Cc: Andrea Arcangeli Cc: Matthew Wilcox Signed-off-by: Linus Torvalds [surenb: backport to 4.19 kernel] Cc: stable@vger.kernel.org # 4.19.x Signed-off-by: Suren Baghdasaryan Signed-off-by: Greg Kroah-Hartman [bwh: Backported to 4.9: - Generic get_user_pages_fast() calls __get_user_pages_fast() here, so make it pass write=1 - Various architectures have their own implementations of get_user_pages_fast(), so apply the corresponding change there - Adjust context] Signed-off-by: Ben Hutchings Signed-off-by: Greg Kroah-Hartman

MIPS: c-r4k: Fix section mismatch for loongson2_sc_init

2021-03-03T16:44:34+00:00

[ Upstream commit c58734eee6a2151ba033c0dcb31902c89e310374 ] When building with clang, the following section mismatch warning occurs: WARNING: modpost: vmlinux.o(.text+0x24490): Section mismatch in reference from the function r4k_cache_init() to the function .init.text:loongson2_sc_init() This should have been fixed with commit ad4fddef5f23 ("mips: fix Section mismatch in reference") but it was missed. Remove the improper __init annotation like that commit did. Fixes: 078a55fc824c ("MIPS: Delete __cpuinit/__CPUINIT usage from MIPS code") Link: https://github.com/ClangBuiltLinux/linux/issues/787 Signed-off-by: Nathan Chancellor Reviewed-by: Huacai Chen Signed-off-by: Thomas Bogendoerfer Signed-off-by: Sasha Levin

MIPS: export has_transparent_hugepage() for modules

2020-11-24T12:03:01+00:00

[ Upstream commit 31b4d8e172f614adc53ddecb4b6b2f6411a49b84 ] MIPS should export its local version of "has_transparent_hugepage" so that loadable modules (dax) can use it. Fixes this build error: ERROR: modpost: "has_transparent_hugepage" [drivers/dax/dax.ko] undefined! Fixes: fd8cfd300019 ("arch: fix has_transparent_hugepage()") Reported-by: kernel test robot Signed-off-by: Randy Dunlap Cc: Thomas Bogendoerfer Cc: linux-mips@vger.kernel.org Cc: Dan Williams Cc: Vishal Verma Cc: Dave Jiang Cc: linux-nvdimm@lists.01.org Cc: Hugh Dickins Cc: Andrew Morton Signed-off-by: Thomas Bogendoerfer Signed-off-by: Sasha Levin

MIPS: mm: BMIPS5000 has inclusive physical caches

2020-09-12T09:47:33+00:00

[ Upstream commit dbfc95f98f0158958d1f1e6bf06d74be38dbd821 ] When the BMIPS generic cpu-feature-overrides.h file was introduced, cpu_has_inclusive_caches/MIPS_CPU_INCLUSIVE_CACHES was not set for BMIPS5000 CPUs. Correct this when we have initialized the MIPS secondary cache successfully. Fixes: f337967d6d87 ("MIPS: BMIPS: Add cpu-feature-overrides.h") Signed-off-by: Florian Fainelli Signed-off-by: Thomas Bogendoerfer Signed-off-by: Sasha Levin

MIPS: tlbex: Fix build_restore_pagemask KScratch restore

2019-10-29T08:15:18+00:00

commit b42aa3fd5957e4daf4b69129e5ce752a2a53e7d6 upstream. build_restore_pagemask() will restore the value of register $1/$at when its restore_scratch argument is non-zero, and aims to do so by filling a branch delay slot. Commit 0b24cae4d535 ("MIPS: Add missing EHB in mtc0 -> mfc0 sequence.") added an EHB instruction (Execution Hazard Barrier) prior to restoring $1 from a KScratch register, in order to resolve a hazard that can result in stale values of the KScratch register being observed. In particular, P-class CPUs from MIPS with out of order execution pipelines such as the P5600 & P6600 are affected. Unfortunately this EHB instruction was inserted in the branch delay slot causing the MFC0 instruction which performs the restoration to no longer execute along with the branch. The result is that the $1 register isn't actually restored, ie. the TLB refill exception handler clobbers it - which is exactly the problem the EHB is meant to avoid for the P-class CPUs. Similarly build_get_pgd_vmalloc() will restore the value of $1/$at when its mode argument equals refill_scratch, and suffers from the same problem. Fix this by in both cases moving the EHB earlier in the emitted code. There's no reason it needs to immediately precede the MFC0 - it simply needs to be between the MTC0 & MFC0. This bug only affects Cavium Octeon systems which use build_fast_tlb_refill_handler(). Signed-off-by: Paul Burton Fixes: 0b24cae4d535 ("MIPS: Add missing EHB in mtc0 -> mfc0 sequence.") Cc: Dmitry Korotin Cc: stable@vger.kernel.org # v3.15+ Cc: linux-mips@vger.kernel.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Greg Kroah-Hartman

MIPS: tlbex: Explicitly cast _PAGE_NO_EXEC to a boolean

2019-10-07T16:53:15+00:00

[ Upstream commit c59ae0a1055127dd3828a88e111a0db59b254104 ] clang warns: arch/mips/mm/tlbex.c:634:19: error: use of logical '&&' with constant operand [-Werror,-Wconstant-logical-operand] if (cpu_has_rixi && _PAGE_NO_EXEC) { ^ ~~~~~~~~~~~~~ arch/mips/mm/tlbex.c:634:19: note: use '&' for a bitwise operation if (cpu_has_rixi && _PAGE_NO_EXEC) { ^~ & arch/mips/mm/tlbex.c:634:19: note: remove constant to silence this warning if (cpu_has_rixi && _PAGE_NO_EXEC) { ~^~~~~~~~~~~~~~~~ 1 error generated. Explicitly cast this value to a boolean so that clang understands we intend for this to be a non-zero value. Fixes: 00bf1c691d08 ("MIPS: tlbex: Avoid placing software PTE bits in Entry* PFN fields") Link: https://github.com/ClangBuiltLinux/linux/issues/609 Signed-off-by: Nathan Chancellor Signed-off-by: Paul Burton Cc: Ralf Baechle Cc: James Hogan Cc: Nick Desaulniers Cc: linux-mips@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: clang-built-linux@googlegroups.com Signed-off-by: Sasha Levin

MIPS: Add missing EHB in mtc0 -> mfc0 sequence.

2019-07-10T07:55:47+00:00

commit 0b24cae4d535045f4c9e177aa228d4e97bad212c upstream. Add a missing EHB (Execution Hazard Barrier) in mtc0 -> mfc0 sequence. Without this execution hazard barrier it's possible for the value read back from the KScratch register to be the value from before the mtc0. Reproducible on P5600 & P6600. The hazard is documented in the MIPS Architecture Reference Manual Vol. III: MIPS32/microMIPS32 Privileged Resource Architecture (MD00088), rev 6.03 table 8.1 which includes: Producer | Consumer | Hazard ----------|----------|---------------------------- mtc0 | mfc0 | any coprocessor 0 register Signed-off-by: Dmitry Korotin [paul.burton@mips.com: - Commit message tweaks. - Add Fixes tags. - Mark for stable back to v3.15 where P5600 support was introduced.] Signed-off-by: Paul Burton Fixes: 3d8bfdd03072 ("MIPS: Use C0_KScratch (if present) to hold PGD pointer.") Fixes: 829dcc0a956a ("MIPS: Add MIPS P5600 probe support") Cc: linux-mips@vger.kernel.org Cc: stable@vger.kernel.org # v3.15+ Signed-off-by: Greg Kroah-Hartman

MIPS: WARN_ON invalid DMA cache maintenance, not BUG_ON

2018-09-19T20:47:16+00:00

[ Upstream commit d4da0e97baea8768b3d66ccef3967bebd50dfc3b ] If a driver causes DMA cache maintenance with a zero length then we currently BUG and kill the kernel. As this is a scenario that we may well be able to recover from, WARN & return in the condition instead. Signed-off-by: Paul Burton Acked-by: Florian Fainelli Patchwork: https://patchwork.linux-mips.org/patch/14623/ Cc: Ralf Baechle Cc: linux-mips@linux-mips.org Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

MIPS: Fix ioremap() RAM check

2018-07-17T09:37:51+00:00

commit 523402fa9101090c91d2033b7ebdfdcf65880488 upstream. 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 Reported-by: Serge Semin Tested-by: Serge Semin Fixes: 92923ca3aace ("mm: meminit: only set page reserved in the memblock region") Cc: James Hogan Cc: Ralf Baechle Cc: linux-mips@linux-mips.org Cc: stable@vger.kernel.org # v4.2+ Patchwork: https://patchwork.linux-mips.org/patch/19786/ Signed-off-by: Greg Kroah-Hartman