On Thu, Feb 11, 2016 at 2:58 PM, Andrew Cooper <andrew.coop...@citrix.com>
wrote:
> On 11/02/2016 21:49, Razvan Cojocaru wrote:
> > On 02/11/2016 11:35 PM, Andrew Cooper wrote:
> >> On 11/02/2016 21:05, Tamas K Lengyel wrote:
> >>
> >>> diff --git a/xen/arch/x86/vm_event.c b/xen/arch/x86/vm_event.c
> >>> index 08d678a..fa5d154 100644
> >>> --- a/xen/arch/x86/vm_event.c
> >>> +++ b/xen/arch/x86/vm_event.c
> >>> @@ -122,6 +122,64 @@ void vm_event_set_registers(struct vcpu *v,
> vm_event_response_t *rsp)
> >>> v->arch.user_regs.eip = rsp->data.regs.x86.rip;
> >>> }
> >>>
> >>> +void vm_event_fill_regs(vm_event_request_t *req)
> >>> +{
> >>> + const struct cpu_user_regs *regs = guest_cpu_user_regs();
> >>> + struct segment_register seg;
> >>> + struct hvm_hw_cpu ctxt;
> >>> + struct vcpu *curr = current;
> >>> +
> >>> + req->data.regs.x86.rax = regs->eax;
> >>> + req->data.regs.x86.rcx = regs->ecx;
> >>> + req->data.regs.x86.rdx = regs->edx;
> >>> + req->data.regs.x86.rbx = regs->ebx;
> >>> + req->data.regs.x86.rsp = regs->esp;
> >>> + req->data.regs.x86.rbp = regs->ebp;
> >>> + req->data.regs.x86.rsi = regs->esi;
> >>> + req->data.regs.x86.rdi = regs->edi;
> >>> +
> >>> + req->data.regs.x86.r8 = regs->r8;
> >>> + req->data.regs.x86.r9 = regs->r9;
> >>> + req->data.regs.x86.r10 = regs->r10;
> >>> + req->data.regs.x86.r11 = regs->r11;
> >>> + req->data.regs.x86.r12 = regs->r12;
> >>> + req->data.regs.x86.r13 = regs->r13;
> >>> + req->data.regs.x86.r14 = regs->r14;
> >>> + req->data.regs.x86.r15 = regs->r15;
> >>> +
> >>> + req->data.regs.x86.rflags = regs->eflags;
> >>> + req->data.regs.x86.rip = regs->eip;
> >>> + req->data.regs.x86.dr7 = curr->arch.debugreg[7];
> >> I think there is a %dr7 handling issue here. For an HVM guests, this
> >> field is only valid when you are not in the context of the guest, as it
> >> lives in the vmcs/vmcs. (PV guests keep it synchronously up to date)
> > Would this make it OK to use in p2m_vm_event_fill_regs() but not in
> > hvm_event_fill_regs(), as it currently is? Maybe this is the issue I'm
> > remembering.
>
> Its use in p2m_mem_access_check() looks similarly buggy. That is also
> in the context of 'current'.
>
> I would have thought that the use of hardware debugging facilities would
> be rare in the general case, which probably means that by chance, the
> value is right most of the time (as it gets synchronised when a vcpu is
> scheduled on a new pcpu).
>
This is an issue that should be addressed in a separate patch. It does look
like dr7 will need a separate hvm function we can call to do a __vmread for
us on GUEST_DR7.
Tamas
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