Re: [Xen-devel] [PATCH v7 11/19] x86/VPMU: Interface for setting PMU mode and flags

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 06/11/2014 06:14 AM, Jan Beulich wrote:
> > > > On 06.06.14 at 19:40, <boris.ostrovsky@xxxxxxxxxx> wrote:
> > --- a/xen/arch/x86/x86_64/compat/entry.S
> > +++ b/xen/arch/x86/x86_64/compat/entry.S
> > @@ -417,6 +417,8 @@ ENTRY(compat_hypercall_table)
> >           .quad do_domctl
> >           .quad compat_kexec_op
> >           .quad do_tmem_op
> > +        .quad do_ni_hypercall           /* reserved for XenClient */
> > +        .quad do_xenpmu_op              /* 40 */
> >           .rept __HYPERVISOR_arch_0-((.-compat_hypercall_table)/8)
> >           .quad compat_ni_hypercall
> >           .endr
> > @@ -465,6 +467,8 @@ ENTRY(compat_hypercall_args_table)
> >           .byte 1 /* do_domctl                */
> >           .byte 2 /* compat_kexec_op          */
> >           .byte 1 /* do_tmem_op               */
> > +        .byte 0 /* reserved for XenClient   */
> > +        .byte 2 /* do_xenpmu_op             */  /* 40 */
> >           .rept __HYPERVISOR_arch_0-(.-compat_hypercall_args_table)
> >           .byte 0 /* compat_ni_hypercall      */
> >           .endr
> I'm pretty certain I said on an earlier version of the patch series
> already: If you use the same handler for native and compat mode
> hypercalls, you should add structure layout verification (see the ?
> entries in xen/include/xlat.lst and how what they produce is being
> used in various places). And the fact that the interface structure
> contains a handle already makes clear that this check will fail - I
> don't think there's  a way around having at least a thin compat
> mode wrapper here.

Right. And I decided to drop the handle since noone is using it now 
anyway and I don't want to add a compat layer for something that may 
never get used.
I have a question though. I want to add a compat check for

struct xen_pmu_arch {
    union {
        struct cpu_user_regs regs;
        uint8_t pad[256];
    } r;
    union {
        uint32_t lapic_lvtpc;
        uint64_t pad;
    } l;
    union {
        struct xen_pmu_amd_ctxt amd;
        struct xen_pmu_intel_ctxt intel;
        uint8_t pad[128];
    } c;
};

which is a shared structure (i.e. it's not used across a hypercall). The 
problem I am having is that cpu_user_regs needs to be translated. Does 
the xlat framework allow checking a structure that needs one of its 
fields translated? I went through the scripts and it appears that it 
doesn't.
Thanks.
-boris

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