linux-kernel - [PATCH 1/3] lguest: fix sense if IF flag on interrupt injection

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Message-Id: <1184933473.10380.296.camel@localhost.localdomain>
Date:	Fri, 20 Jul 2007 22:11:13 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
	virtualization <virtualization@...ts.linux-foundation.org>
Subject: [PATCH 1/3] lguest: fix sense if IF flag on interrupt injection

The sense of the IF bit is backwards in the host interrupt handling.

This means we always save "IF=1" on the stack when injecting an
interrupt.  It turns out this is almost always correct (unless the
guest is taking a page fault in an interrupt due to an unpopulated
vmalloc mapping), so went unnoticed.

Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
---
 drivers/lguest/interrupts_and_traps.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff -r 209f5cd5cda5 drivers/lguest/interrupts_and_traps.c
--- a/drivers/lguest/interrupts_and_traps.c	Fri Jul 20 14:53:40 2007 +1000
+++ b/drivers/lguest/interrupts_and_traps.c	Fri Jul 20 21:34:06 2007 +1000
@@ -38,12 +38,12 @@ static void set_guest_interrupt(struct l
 		ss = lg->regs->ss;
 	}
 
-	/* We use IF bit in eflags to indicate whether irqs were disabled
-	   (it's always 0, since irqs are enabled when guest is running). */
+	/* We use IF bit in eflags to indicate whether irqs were enabled
+	   (it's always 1, since irqs are enabled when guest is running). */
 	eflags = lg->regs->eflags;
-	if (get_user(irq_enable, &lg->lguest_data->irq_enabled))
-		irq_enable = 0;
-	eflags |= (irq_enable & X86_EFLAGS_IF);
+	if (get_user(irq_enable, &lg->lguest_data->irq_enabled) == 0
+	    && !(irq_enable & X86_EFLAGS_IF))
+		eflags &= ~X86_EFLAGS_IF;
 
 	push_guest_stack(lg, &gstack, eflags);
 	push_guest_stack(lg, &gstack, lg->regs->cs);


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