On 08/06/18 14:00, Jan Beulich wrote:
>>>> On 04.06.18 at 15:59, <andrew.coop...@citrix.com> wrote:
>> --- a/xen/arch/x86/hvm/svm/svm.c
>> +++ b/xen/arch/x86/hvm/svm/svm.c
>> @@ -1437,19 +1437,49 @@ static void svm_inject_event(const struct x86_event
>> *event)
>> switch ( _event.vector | -(_event.type == X86_EVENTTYPE_SW_INTERRUPT) )
>> {
>> case TRAP_debug:
>> - if ( regs->eflags & X86_EFLAGS_TF )
>> - {
>> - __restore_debug_registers(vmcb, curr);
>> - vmcb_set_dr6(vmcb, vmcb_get_dr6(vmcb) | DR_STEP);
>> - }
>> + /*
>> + * On AMD hardware, a #DB exception:
>> + * 1) Merges new status bits into %dr6
>> + * 2) Clears %dr7.gd and MSR_DEBUGCTL.{LBR,BTF}
>> + *
>> + * Item 1 is done by hardware before a #DB intercepted vmexit, but
>> we
>> + * may end up here from emulation so have to repeat it ourselves.
>> + * Item 2 is done by hardware when injecting a #DB exception.
>> + */
>> + __restore_debug_registers(vmcb, curr);
>> + vmcb_set_dr6(vmcb, vmcb_get_dr6(vmcb) | event->pending_dbg);
>> +
>> /* fall through */
>> case TRAP_int3:
>> if ( curr->domain->debugger_attached )
>> {
>> /* Debug/Int3: Trap to debugger. */
>> + if ( _event.vector == TRAP_int3 )
>> + {
>> + /* N.B. Can't use __update_guest_eip() for risk of
>> recusion. */
>> + regs->rip += _event.insn_len;
> Not all callers provide a non-zero insn length. Is that a potential
> problem here (and in the equivalent VMX code)?
TRAP_int3 is strictly a software exception (and/or software interrupt if
started via `int $n`), so should always have a nonzero length.
We should be able to assert this property, and I was considering some
extra checks in the {pv,hvm}_inject_event() logic, although it would
require XEN_DMOP_inject_event gaining more sanity checking than it
currently has (which is probably a good thing).
I'll fold something suitable into v2, which is already quite a bit
longer to help with monitor problem identified here.
>> @@ -2775,67 +2805,46 @@ void svm_vmexit_handler(struct cpu_user_regs *regs)
>>
>> case VMEXIT_ICEBP:
>> case VMEXIT_EXCEPTION_DB:
>> - if ( !v->domain->debugger_attached )
>> + case VMEXIT_EXCEPTION_BP:
>> + {
>> + unsigned int vec, type, len, extra;
>> +
>> + switch ( exit_reason )
>> {
>> - int rc;
>> - unsigned int trap_type;
>> + case VMEXIT_ICEBP:
> I don't understand this structuring of the code: The outer switch()
> has the exact same control expression, and there's no fall through
> - why the nesting? Move the variable declarations to the beginning
> of the outer switch() and drop the inner one? You may not even
> need all of the variables if you replicated the little bit of code
> currently shared by the three (immediately after the inner switch()).
Good question - I think this layout is a side effect of me changing my
mind several times during its development.
~Andrew
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