Re: [cleanup] do_general_protection doesn't disable irq

From: Karsten Keil (kkeil_at_suse.de)
Date: 07/30/04

  • Next message: Shane Shrybman: "Re: [patch] voluntary-preempt-2.6.8-rc2-L2 PS2 keyboard gone south" 
    Date:	Fri, 30 Jul 2004 15:58:40 +0200
To: Linux Kernel list <linux-kernel@vger.kernel.org>

    On Fri, Jul 30, 2004 at 12:22:05AM -0400, Brian Gerst wrote:
    > Andrea Arcangeli wrote:
    > >A trap gate shouldn't affect the irq status at all.
    > >
    > >This should be a valid cleanup that removes a slightly confusing noop:
    > >
    > >Index: linux-2.5/arch/i386/kernel/traps.c
    > >===================================================================
    > >RCS file: /home/andrea/crypto/cvs/linux-2.5/arch/i386/kernel/traps.c,v
    > >retrieving revision 1.77
    > >diff -u -p -r1.77 traps.c
    > >--- linux-2.5/arch/i386/kernel/traps.c 13 Jul 2004 18:02:33 -0000
    > >1.77
    > >+++ linux-2.5/arch/i386/kernel/traps.c 30 Jul 2004 02:44:23 -0000
    > >@@ -431,9 +431,6 @@ DO_ERROR_INFO(17, SIGBUS, "alignment che
    > >
    > > asmlinkage void do_general_protection(struct pt_regs * regs, long
    > > error_code)
    > > {
    > >- if (regs->eflags & X86_EFLAGS_IF)
    > >- local_irq_enable();
    > >-
    > > if (regs->eflags & VM_MASK)
    > > goto gp_in_vm86;
    > >
    > >
    > >Thanks to Karsten for noticing a trap gate doesn't actually enable irq
    > >by default either (offtopic issue with the above patch, but while
    > >reading the 2.6 code I found the above bit which just confused me more
    > >since it's a noop, either that or you meant to use set_intr_gate, not
    > >set_trap_gate on the do_general_protection handler, but it seems not
    > >needed to use a trap gate since a trap gate shouldn't enable irqs by
    > >default). Please correct me if wrong.
    >
    > This is there for vm86 mode. See http://tinyurl.com/3m5nr
    >

    It makes also no sense, if the GP comes from VM86 mode, what you
    need there is the second hunk in the patch which does local_irq_enable();
    if it was from VM86. Note: the trap gate do not touch X86_EFLAGS_IF bit,
    so the saved value in regs->eflags is the same as in the CPU EFLAGS register. 

    -- 
Karsten Keil
SuSE Labs
ISDN development
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/
  • Next message: Shane Shrybman: "Re: [patch] voluntary-preempt-2.6.8-rc2-L2 PS2 keyboard gone south"

    Relevant Pages