linux-kernel - [014/101] xen: x86_32: do not enable iterrupts when returning from exception in interrupt context

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Message-Id: <20111102222740.954115104@clark.kroah.org>
Date:	Wed, 02 Nov 2011 15:25:58 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Igor Mammedov <imammedo@...hat.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: [014/101] xen: x86_32: do not enable iterrupts when returning from exception in interrupt context

2.6.33-longterm review patch.  If anyone has any objections, please let us know.

------------------

From: Igor Mammedov <imammedo@...hat.com>

commit d198d499148a0c64a41b3aba9e7dd43772832b91 upstream.

If vmalloc page_fault happens inside of interrupt handler with interrupts
disabled then on exit path from exception handler when there is no pending
interrupts, the following code (arch/x86/xen/xen-asm_32.S:112):

	cmpw $0x0001, XEN_vcpu_info_pending(%eax)
	sete XEN_vcpu_info_mask(%eax)

will enable interrupts even if they has been previously disabled according to
eflags from the bounce frame (arch/x86/xen/xen-asm_32.S:99)

	testb $X86_EFLAGS_IF>>8, 8+1+ESP_OFFSET(%esp)
	setz XEN_vcpu_info_mask(%eax)

Solution is in setting XEN_vcpu_info_mask only when it should be set
according to
	cmpw $0x0001, XEN_vcpu_info_pending(%eax)
but not clearing it if there isn't any pending events.

Reproducer for bug is attached to RHBZ 707552

Signed-off-by: Igor Mammedov <imammedo@...hat.com>
Acked-by: Jeremy Fitzhardinge <jeremy@...p.org>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 arch/x86/xen/xen-asm_32.S |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/arch/x86/xen/xen-asm_32.S
+++ b/arch/x86/xen/xen-asm_32.S
@@ -113,11 +113,13 @@ xen_iret_start_crit:
 
 	/*
 	 * If there's something pending, mask events again so we can
-	 * jump back into xen_hypervisor_callback
+	 * jump back into xen_hypervisor_callback. Otherwise do not
+	 * touch XEN_vcpu_info_mask.
 	 */
-	sete XEN_vcpu_info_mask(%eax)
+	jne 1f
+	movb $1, XEN_vcpu_info_mask(%eax)
 
-	popl %eax
+1:	popl %eax
 
 	/*
 	 * From this point on the registers are restored and the stack


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