linux-kernel - Re: [PATCH v2] xen: x86_32: do not enable iterrupts when returning from exception in interrupt context

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Date:	Thu, 1 Sep 2011 11:45:03 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Igor Mammedov <imammedo@...hat.com>
Cc:	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	jeremy@...p.org
Subject: Re: [PATCH v2] xen: x86_32: do not enable iterrupts when returning
 from exception in interrupt context

On Thu, Sep 01, 2011 at 01:46:55PM +0200, Igor Mammedov wrote:
> 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>
> Signed-off-by: Jeremy Fitzhardinge <jeremy@...p.org>

Stuck it in the queue for 3.1 and stable. Thanks for finding this one!
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