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    • Michael Neuling's avatar
      powerpc/signals: Mark VSX not saved with small contexts · c13f20ac
      Michael Neuling authored
      
      
      The VSX MSR bit in the user context indicates if the context contains VSX
      state.  Currently we set this when the process has touched VSX at any stage.
      
      Unfortunately, if the user has not provided enough space to save the VSX state,
      we can't save it but we currently still set the MSR VSX bit.
      
      This patch changes this to clear the MSR VSX bit when the user doesn't provide
      enough space.  This indicates that there is no valid VSX state in the user
      context.
      
      This is needed to support get/set/make/swapcontext for applications that use
      VSX but only provide a small context.  For example, getcontext in glibc
      provides a smaller context since the VSX registers don't need to be saved over
      the glibc function call.  But since the program calling getcontext may have
      used VSX, the kernel currently says the VSX state is valid when it's not.  If
      the returned context is then used in setcontext (ie. a small context without
      VSX but with MSR VSX set), the kernel will refuse the context.  This situation
      has been reported by the glibc community.
      
      Based on patch from Carlos O'Donell.
      
      Tested-by: default avatarHaren Myneni <haren@linux.vnet.ibm.com>
      Signed-off-by: default avatarMichael Neuling <mikey@neuling.org>
      Cc: stable@vger.kernel.org
      Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
      c13f20ac