Re: [Xen-devel] [PATCH RFC] pvh: clearly specify used parameters in vcpu_guest_context

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

On Fri, 15 Nov 2013 16:45:47 +0000
"Jan Beulich" <JBeulich@xxxxxxxx> wrote:

> >>> On 15.11.13 at 17:40, George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> >>> wrote:
> > On 15/11/13 16:32, Jan Beulich wrote:
> >>>>> On 15.11.13 at 16:50, Roger Pau Monne <roger.pau@xxxxxxxxxx>
> >>>>> wrote:
> >>> --- a/xen/arch/x86/domain.c
> >>> +++ b/xen/arch/x86/domain.c
> >>> @@ -704,9 +704,11 @@ int arch_set_info_guest(
> >>>           /* PVH 32bitfixme */
> >>>           ASSERT(!compat);
> >>>   
> >>> -        if ( c(ctrlreg[1]) || c(ldt_base) || c(ldt_ents) ||
> >>> +        if ( c(ctrlreg[0]) || c(ctrlreg[1]) || c(ctrlreg[2]) ||
> >>> +             c(ctrlreg[4]) || c(ldt_base) || c(ldt_ents) ||
> >> I think it should actually be a bug for the guest to request an
> >> all blank CR0 or CR4. Minimally CR0.PE, CR0.PG, and CR4.PAE
> >> would seem to be a valid requirement to be set.
> >>
> >> Apart from that ctrlreg[] is an 8-element array... And I don't
> >> see debugreg[] being verified at all.
> >>
> >>>                c(user_regs.cs) || c(user_regs.ss) ||
> >>> c(user_regs.es) || c(user_regs.ds) || c(user_regs.fs) ||
> >>> c(user_regs.gs) ||
> >>> +             c(kernel_ss) || c(kernel_sp) ||
> >>> c.nat->gs_base_kernel ||
> >> So George and/or Mukesh found it necessary to set
> >> gs_base_kernel, and you rip it out? I'm curious as to what
> >> they're going to say...
> > 
> > I didn't find it necessary; I was mostly focused on merging the PVH
> > and HVM codepaths without causing any regressions.  It's not
> > obvious to me what's special about gs_base_kernel, and I haven't
> > yet gone back to try to find out why Mukesh did it that way.

Hi,

We had talked about this while ago, but upon boot, the first thing
a vcpu needs is access to kernel data structure. (A secondary vcpu
is bootstrapped way up into the kernel). It would be possible to
get rid of gs_base_kernel, but will take some work on the linux side. 
I can try and test it out, and let you guys know.

thanks
mukesh

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