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Miller" , Borislav Petkov , Ingo Molnar Subject: Re: [PATCH v4 2/2] vmalloc: Avoid rare case of flushing tlb with weird arguements Message-ID: <20190527122425.GQ2606@hirez.programming.kicks-ass.net> References: <20190521205137.22029-1-rick.p.edgecombe@intel.com> <20190521205137.22029-3-rick.p.edgecombe@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190521205137.22029-3-rick.p.edgecombe@intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, May 21, 2019 at 01:51:37PM -0700, Rick Edgecombe wrote: > In a rare case, flush_tlb_kernel_range() could be called with a start > higher than the end. Most architectures should be fine with with this, but > some may not like it, so avoid doing this. > > In vm_remove_mappings(), in case page_address() returns 0 for all pages, > _vm_unmap_aliases() will be called with start = ULONG_MAX, end = 0 and > flush = 1. > > If at the same time, the vmalloc purge operation is triggered by something > else while the current operation is between remove_vm_area() and > _vm_unmap_aliases(), then the vm mapping just removed will be already > purged. In this case the call of vm_unmap_aliases() may not find any other > mappings to flush and so end up flushing start = ULONG_MAX, end = 0. So > only set flush = true if we find something in the direct mapping that we > need to flush, and this way this can't happen. > > Fixes: 868b104d7379 ("mm/vmalloc: Add flag for freeing of special permsissions") > Cc: Meelis Roos > Cc: Peter Zijlstra > Cc: "David S. Miller" > Cc: Dave Hansen > Cc: Borislav Petkov > Cc: Andy Lutomirski > Cc: Ingo Molnar > Cc: Nadav Amit > Signed-off-by: Rick Edgecombe > --- > mm/vmalloc.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index 836888ae01f6..537d1134b40e 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -2125,6 +2125,7 @@ static void vm_remove_mappings(struct vm_struct *area, int deallocate_pages) > unsigned long addr = (unsigned long)area->addr; > unsigned long start = ULONG_MAX, end = 0; > int flush_reset = area->flags & VM_FLUSH_RESET_PERMS; > + int flush_dmap = 0; > int i; > > /* > @@ -2163,6 +2164,7 @@ static void vm_remove_mappings(struct vm_struct *area, int deallocate_pages) > if (addr) { > start = min(addr, start); > end = max(addr + PAGE_SIZE, end); > + flush_dmap = 1; > } > } > > @@ -2172,7 +2174,7 @@ static void vm_remove_mappings(struct vm_struct *area, int deallocate_pages) > * reset the direct map permissions to the default. > */ > set_area_direct_map(area, set_direct_map_invalid_noflush); > - _vm_unmap_aliases(start, end, 1); > + _vm_unmap_aliases(start, end, flush_dmap); > set_area_direct_map(area, set_direct_map_default_noflush); > } Hurmph.. another clue that this range flushing is crap I feel. The phys addrs of the page array can be scattered all over the place, a range doesn't properly represent things. But yes, this seems like a minimal fix in spirit with the existing code.