Re: [Xen-devel] [PATCH 2/5] xen/x86-64: clean up warnings aboutIST-using traps

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

>>> Jeremy Fitzhardinge <jeremy@xxxxxxxx> 07.05.09 20:56 >>>
>Ignore known IST-using traps.  Aside from the debugger traps, they're
>low-level faults which Xen will handle for us, so the kernel needn't
>worry about them.  Keep warning in case unknown trap starts using IST.
>
>Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
>---
> arch/x86/xen/enlighten.c |   22 ++++++++++++++++++++--
> 1 files changed, 20 insertions(+), 2 deletions(-)
>
>diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
>index cb49f57..88f3aa4 100644
>--- a/arch/x86/xen/enlighten.c
>+++ b/arch/x86/xen/enlighten.c
>@@ -439,12 +439,30 @@ static int cvt_gate_to_trap(int vector, const gate_desc 
>*val,
> 
>       addr = gate_offset(*val);
> #ifdef CONFIG_X86_64
>+      /*
>+       * Look for known traps using IST, and substitute them
>+       * appropriately.  The debugger ones are the only ones we care
>+       * about.  Xen will handle faults like double_fault and
>+       * machine_check, so we should never see them.  Warn if
>+       * there's an unexpected IST-using fault handler.
>+       */
>       if (addr == (unsigned long)debug)
>               addr = (unsigned long)xen_debug;
>       else if (addr == (unsigned long)int3)
>               addr = (unsigned long)xen_int3;
>-      else
>-              WARN_ON(val->ist != 0);
>+      else if (addr == (unsigned long)double_fault ||
>+               addr == (unsigned long)stack_segment) {

I don't think you want to exclude handling stack faults: Ordinary memory
references using rsp or rbp as the base register will cause these instead
of general protection faults when the resulting effective address is non-
canonical.

>+              /* Don't need to handle these */
>+              return 0;
>+#ifdef CONFIG_X86_MCE
>+      } else if (addr == (unsigned long)machine_check) {
>+              return 0;
>+#endif
>+      } else {
>+              /* Some other trap using IST? */
>+              if (WARN_ON(val->ist != 0))
>+                      return 0;
>+      }
> #endif        /* CONFIG_X86_64 */
>       info->address = addr;
> 
>-- 
>1.6.0.6

Jan


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