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SubjectRe: [Xen-devel] [PATCH 2/5] xen/x86-64: clean up warnings aboutIST-using traps
>>> Jeremy Fitzhardinge <jeremy@goop.org> 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@citrix.com>
>---
> 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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