On Thu, Jan 28, 2016 at 2:05 PM, Razvan Cojocaru <rcojoc...@bitdefender.com> wrote:
> On 01/28/2016 10:09 PM, Tamas K Lengyel wrote: > > On Thu, Jan 28, 2016 at 6:52 AM, Razvan Cojocaru > > <rcojoc...@bitdefender.com <mailto:rcojoc...@bitdefender.com>> 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. Tamas
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