[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v7 10/10] x86/vm_event: Carry Processor Trace buffer offset in vm_event
On Fri, Jan 29, 2021 at 6:22 PM Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote: > > On 26/01/2021 14:27, Jan Beulich wrote: > > On 21.01.2021 22:27, Andrew Cooper wrote: > >> --- a/xen/arch/x86/vm_event.c > >> +++ b/xen/arch/x86/vm_event.c > >> @@ -251,6 +251,9 @@ void vm_event_fill_regs(vm_event_request_t *req) > >> > >> req->data.regs.x86.shadow_gs = ctxt.shadow_gs; > >> req->data.regs.x86.dr6 = ctxt.dr6; > >> + > >> + if ( hvm_vmtrace_output_position(curr, &req->data.regs.x86.pt_offset) > >> != 1 ) > >> + req->data.regs.x86.pt_offset = ~0; > > Ah. (Regarding my earlier question about this returning -errno or > > boolean). > > > >> --- a/xen/include/public/vm_event.h > >> +++ b/xen/include/public/vm_event.h > >> @@ -223,6 +223,12 @@ struct vm_event_regs_x86 { > >> */ > >> uint64_t npt_base; > >> > >> + /* > >> + * Current offset in the Processor Trace buffer. For Intel Processor > >> Trace > >> + * this is MSR_RTIT_OUTPUT_MASK. Set to ~0 if no Processor Trace is > >> active. > >> + */ > >> + uint64_t pt_offset; > > According to vmtrace_output_position() the value is only one half > > of what the named MSR contains. Perhaps "... this is from MSR_..."? > > Not sure whether, despite this, there still is a reason to have > > this 64-bit wide. > > This is a vestigial remnant which escaped the "use vmtrace uniformly" work. > > It should match the domctl_vmtrace_output_position() format, so each > interface gives the same content for the attempted-platform-neutral version. >From the vm_event ABI perspective it's simpler to have a 64-bit value here even if the max value it may possibly carry is never going to use the whole 64-bit width. I rather not play with shortening it just to add padding somewhere else. As for what it's called is not that important from my perspective, vmtrace_pos or something like that for example is fine by me. Tamas
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