Messages in this thread | | | From | Andy Lutomirski <> | Date | Wed, 26 Jul 2017 06:48:42 -0700 | Subject | Re: [PATCH v1] xen: get rid of paravirt op adjust_exception_frame |
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On Mon, Jul 24, 2017 at 7:28 AM, Juergen Gross <jgross@suse.com> wrote: > When running as Xen pv-guest the exception frame on the stack contains > %r11 and %rcx additional to the other data pushed by the processor. > > Instead of having a paravirt op being called for each exception type > prepend the Xen specific code to each exception entry. When running as > Xen pv-guest just use the exception entry with prepended instructions, > otherwise use the entry without the Xen specific code.
I think this is a nice cleanup, but I'm wondering if it would be even nicer if the Xen part was kept out-of-line. That is, could Xen have little stubs like:
xen_alignment_check: pop %rcx pop %r11 jmp alignment_check
rather than using the macros in entry_64.S that you have? Then you could adjust set_trap_gate instead of pack_gate and maybe even do something like:
#define set_trap_gate(..., name, ...) set_native_or_xen_trap_gate(..., name, xen_##name, ...)
> /* Runs on exception stack */ > -ENTRY(nmi) > - /* > - * Fix up the exception frame if we're on Xen. > - * PARAVIRT_ADJUST_EXCEPTION_FRAME is guaranteed to push at most > - * one value to the stack on native, so it may clobber the rdx > - * scratch slot, but it won't clobber any of the important > - * slots past it. > - * > - * Xen is a different story, because the Xen frame itself overlaps > - * the "NMI executing" variable. > - */
I would keep this comment. The Xen frame really is in the way AFAICT.
--Andy
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