aminfar aminfar - 1 month ago 13
Linux Question

Flush cpu cache for a region of address space

I am interested in flushing cache (L1, L2, and L3) only for a region of address space, for example all cache entries from address A to address B. Is there a mechanism to do so in linux?

Answer

Check this page for list of available flushing methods in linux kernel: https://www.kernel.org/doc/Documentation/cachetlb.txt

Cache and TLB Flushing Under Linux. David S. Miller

There are set of range flushing functions

2) flush_cache_range(vma, start, end);
   change_range_of_page_tables(mm, start, end);
   flush_tlb_range(vma, start, end);

3) void flush_cache_range(struct vm_area_struct *vma, unsigned long start, unsigned long end)

Here we are flushing a specific range of (user) virtual
addresses from the cache.  After running, there will be no
entries in the cache for 'vma->vm_mm' for virtual addresses in
the range 'start' to 'end-1'.

You can also check implementation of the function - http://lxr.free-electrons.com/ident?a=sh;i=flush_cache_range

For example, in arm - http://lxr.free-electrons.com/source/arch/arm/mm/flush.c?a=sh&v=3.13#L67

 67 void flush_cache_range(struct vm_area_struct *vma, unsigned long start, unsigned long end)
 68 {
 69         if (cache_is_vivt()) {
 70                 vivt_flush_cache_range(vma, start, end);
 71                 return;
 72         }
 73 
 74         if (cache_is_vipt_aliasing()) {
 75                 asm(    "mcr    p15, 0, %0, c7, c14, 0\n"
 76                 "       mcr     p15, 0, %0, c7, c10, 4"
 77                     :
 78                     : "r" (0)
 79                     : "cc");
 80         }
 81 
 82         if (vma->vm_flags & VM_EXEC)
 83                 __flush_icache_all();
 84 }
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