>>> On 18.12.15 at 11:18, <david.vra...@citrix.com> wrote: > On 18/12/15 07:53, Tian, Kevin wrote: >>> From: David Vrabel [mailto:david.vra...@citrix.com] >>> Sent: Thursday, December 17, 2015 11:17 PM >> >> [...] >> >>> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c >>> index f7c5e4f..cca35f2 100644 >>> --- a/xen/arch/x86/hvm/vmx/vmx.c >>> +++ b/xen/arch/x86/hvm/vmx/vmx.c >> >> [...] >> >>> @@ -3507,6 +3495,16 @@ void vmx_vmenter_helper(const struct cpu_user_regs > *regs) >>> if ( unlikely(need_flush) ) >>> vpid_sync_all(); >>> >>> + if ( paging_mode_hap(curr->domain) ) >>> + { >>> + struct ept_data *ept = &p2m_get_hostp2m(curr->domain)->ept; >>> + unsigned int cpu = smp_processor_id(); >>> + >>> + if ( cpumask_test_cpu(cpu, ept->invalidate) >>> + && cpumask_test_and_clear_cpu(cpu, ept->invalidate) ) >> >> Just test_and_clear should be enough. > > The first test is to avoid the locked test and clear in the common case. > But this is probably better written as > > if ( cpumask_test_cpu(cpu, ept->invalidate) ) > { > cpumask_clear_cpu(cpu, ept->invalidate); > __invept(...); > }
The question is what you care for more: Avoiding the invalidation if you lose the race here, or avoiding the extra conditional. (Either is correct in this context afaict.) Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
