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Re: [Xen-devel] [PATCH] vm_event: make sure the domain is paused in key domctls

To: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>

From: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>

Date: Fri, 29 Jan 2016 08:55:06 +0200

Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Keir Fraser <keir@xxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxx>

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List-id: Xen developer discussion <xen-devel.lists.xen.org>

On 01/29/2016 08:52 AM, Razvan Cojocaru wrote: > On 01/28/2016 11:47 PM, Tamas K Lengyel wrote: >> >> >> On Thu, Jan 28, 2016 at 2:05 PM, Razvan Cojocaru >> <rcojocaru@xxxxxxxxxxxxxxx <mailto:rcojocaru@xxxxxxxxxxxxxxx>> wrote: >> >> On 01/28/2016 10:09 PM, Tamas K Lengyel wrote: >> > On Thu, Jan 28, 2016 at 6:52 AM, Razvan Cojocaru >> > <rcojocaru@xxxxxxxxxxxxxxx <mailto:rcojocaru@xxxxxxxxxxxxxxx> >> <mailto:rcojocaru@xxxxxxxxxxxxxxx >> <mailto:rcojocaru@xxxxxxxxxxxxxxx>>> wrote: >> > >> > This patch pauses the domain for all writes through the 'ad' >> > pointer in monitor_domctl(), defers a domain_unpause() call until >> > after the CRs are updated for the MONITOR_EVENT_WRITE_CTRLREG >> > case, and makes sure that the domain is paused for both vm_event >> > enable and disable cases in vm_event_domctl(). >> > Thanks go to Andrew Cooper for his review and suggestions. >> > >> > >> > For vm_event_enable the domain is already paused by libxc before the >> > domctl is issued. I don't see a problem in doing another pause in Xen, >> > but given we have XSA-99, just doing this pause in Xen would not be >> > enough. So is it really necessary/fixes anything? >> >> This isn't about XSA-99, the problem here is related to my previous >> patch "x86 vm_event: reset monitor in vm_event_cleanup_domain()". While >> that improves matters and greatly reduces the chances of crashes due to >> hvm_msr_write_intercept() or hvm_set_crX() dereferencing a NULL >> v->arch.vm_event that's assumed to be OK, when the corresponding >> v->domain->arch.monitor is non-zero, the foolproof way is to make sure >> that functions such as vm_event_cleanup_domain() are always being called >> only while the domain has been paused. So there should be a >> domain_pause() call somewhere on the call path before that. >> >> >> Sure, but that's the disable case. I was only wondering about the enable >> case where the domain is already paused. > > Yes, for the disable case it is functionally redundant. Sorry, I obviously meant "for the enable case". _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel

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