Messages in this thread |  | | Date | Sat, 21 Jan 2023 11:57:12 +0100 | Subject | Re: [PATCH v3 4/4] fs/sysv: Replace kmap() with kmap_local_page() | From | Helge Deller <> |
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On 1/21/23 09:05, Ira Weiny wrote: > Helge Deller wrote: >> On 1/20/23 06:56, Al Viro wrote: >>> On Fri, Jan 20, 2023 at 05:07:48AM +0000, Al Viro wrote: >>>> On Fri, Jan 20, 2023 at 04:54:51AM +0000, Matthew Wilcox wrote: >>>> >>>>>> Sure, but... there's also this: >>>>>> >>>>>> static inline void __kunmap_local(const void *addr) >>>>>> { >>>>>> #ifdef ARCH_HAS_FLUSH_ON_KUNMAP >>>>>> kunmap_flush_on_unmap(addr); >>>>>> #endif >>>>>> } >>>>>> >>>>>> Are you sure that the guts of that thing will be happy with address that is not >>>>>> page-aligned? I've looked there at some point, got scared of parisc (IIRC) >>>>>> MMU details and decided not to rely upon that... >>>>> >>>>> Ugh, PA-RISC (the only implementor) definitely will flush the wrong >>>>> addresses. I think we should do this, as having bugs that only manifest >>>>> on one not-well-tested architecture seems Bad. >>>>> >>>>> static inline void __kunmap_local(const void *addr) >>>>> { >>>>> #ifdef ARCH_HAS_FLUSH_ON_KUNMAP >>>>> - kunmap_flush_on_unmap(addr); >>>>> + kunmap_flush_on_unmap(PAGE_ALIGN_DOWN(addr)); >>>>> #endif >>>>> } >>>> >>>> PTR_ALIGN_DOWN(addr, PAGE_SIZE), perhaps? >>> >>> Anyway, that's a question to parisc folks; I _think_ pdtlb >>> quietly ignores the lower bits of address, so that part seems >>> to be safe, but I wouldn't bet upon that. >> >> No, on PA2.0 (64bit) CPUs the lower bits of the address of pdtlb >> encodes the amount of memory (page size) to be flushed, see: >> http://ftp.parisc-linux.org/docs/arch/parisc2.0.pdf (page 7-106) >> So, the proposed page alignment with e.g. PTR_ALIGN_DON() is needed. >> > > I'm not sure I completely understand. > > First, arn't PAGE_ALIGN_DOWN(addr) and PTR_ALIGN_DOWN(addr, PAGE_SIZE) the > same?
Yes, they are.
> align.h > #define PTR_ALIGN_DOWN(p, a) ((typeof(p))ALIGN_DOWN((unsigned long)(p), (a))) > > mm.h: > #define PAGE_ALIGN_DOWN(addr) ALIGN_DOWN(addr, PAGE_SIZE) > > Did parisc redefine it somewhere I'm not seeing?
No, there is nothing special in this regard on parisc.
> Second, if the lower bits encode the amount of memory to be flushed is it > required to return the original value returned from page_address()?
No. If the lower bits are zero, then the default page size (4k) is used for the tlb purge. So, if you simply strip the lower bits (by using PAGE_ALIGN_DOWN() or ALIGN_DOWN()) you are fine.
Helge
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