>>> On 12.02.16 at 13:57, <tleng...@novetta.com> wrote: > On Feb 12, 2016 02:12, "Jan Beulich" <jbeul...@suse.com> wrote: >> >> >>> On 12.02.16 at 01:22, <tleng...@novetta.com> wrote: >> > Sending the dr7 register during vm_events is useful for various > applications, >> > but the current way the register value is gathered is incorrent. In this >> > patch >> > we extend vmx_vmcs_save so that we get the correct value. >> > >> > Suggested-by: Andrew Cooper <andrew.coop...@citrix.com> >> >> Iirc Andrew suggested ... >> >> > --- a/xen/arch/x86/hvm/vmx/vmx.c >> > +++ b/xen/arch/x86/hvm/vmx/vmx.c >> > @@ -490,6 +490,7 @@ static void vmx_vmcs_save(struct vcpu *v, struct >> > hvm_hw_cpu *c) >> > __vmread(GUEST_SYSENTER_CS, &c->sysenter_cs); >> > __vmread(GUEST_SYSENTER_ESP, &c->sysenter_esp); >> > __vmread(GUEST_SYSENTER_EIP, &c->sysenter_eip); >> > + __vmread(GUEST_DR7, &c->dr7); >> >> ... just when v == current. >> > > Would that check really be necessary? It would complicate the code not just > here but the caller would need to be aware too that in that case dr7 can be > aquired from someplace else. I don't see the harm in just saving dr7 here > in both cases.
Maybe the solution then is for the suggested if() to have an "else"? While, as someone said elsewhere, a few more cycles may not be noticable, why make things slower than they need to be. Plus - what guarantees that the VMCS field isn't stale while the guest isn't running (perhaps it got updated but not sync-ed back yet in anticipation for this to happen during vCPU resume)? Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
