• Aneesh Kumar K.V's avatar
    powerpc/mm/hash: Properly mask the ESID bits when building proto VSID · 79270e0a
    Aneesh Kumar K.V authored
    The proto VSID is built using both the MMU context id and effective
    segment ID (ESID). We should not have overlapping bits between those.
    That could result in us having a VSID collision. With the current code
    we missed masking the top bits of the ESID. This implies for kernel
    address we ended up using the top 4 bits of the ESID as part of the
    proto VSID, which is wrong.
    
    The current code use the top 4 context values (0x7fffc - 0x7ffff) for
    the kernel. With those context IDs used for the kernel, we don't run
    into VSID collisions because we get the same proto VSID irrespective of
    whether we mask the ESID bits or not. eg:
    
      ea         = 0xf000000000000000
      context    = 0x7ffff
    
      w/out masking:
      proto_vsid = (0x7ffff << 6 | 0xf000000000000000 >> 40)
    	     = (0x1ffffc0 | 0xf00000)
    	     =  0x1ffffc0
    
      with masking:
      proto_vsid = (0x7ffff << 6 | ((0xf000000000000000 >> 40) & 0x3f))
    	     = (0x1ffffc0 | (0xf00000 & 0x3f))
    	     =  0x1ffffc0 | 0)
    	     =  0x1ffffc0
    
    So although there is no bug, the code is still overly subtle, so fix it
    to save ourselves pain in future.
    Signed-off-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
    79270e0a
mmu-hash.h 22.5 KB