Re: [Xen-devel] [PATCH 2/2] x86/dmar: zap DMAR signature for dom0 once in TBOOT case

[Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>]

On 2018/8/20 16:30, Jan Beulich wrote:
> > > > On 20.08.18 at 05:32, <zhenzhong.duan@xxxxxxxxxx> wrote:
> > When TBOOT enabled, acpi_parse_dmar() zap a copy of DMAR table rather
> > than the real table, so make it controled by config option based on the
> > fact that we already have done the real zapping in tboot_parse_dmar_table().
> Is this just a cosmetic change, or is there any harm done by the extra
> zapping?
Cosmetic change, I feel it isn't necessory to zap a copy of DMAR table 
which is freed later.
Thanks
Zhenzhong
> > As said above, acpi_parse_dmar() doesn't zaps APCI DMAR signature in
> > real TXT heap table, fix the stale comments.
> >
> > Signed-off-by: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>
> > ---
> >   xen/arch/x86/tboot.c               |    3 +--
> >   xen/drivers/passthrough/vtd/dmar.c |    2 ++
> >   2 files changed, 3 insertions(+), 2 deletions(-)
> You've again failed to Cc maintainers (included now).
>
> Jan
>
> > --- a/xen/arch/x86/tboot.c
> > +++ b/xen/arch/x86/tboot.c
> > @@ -490,8 +490,7 @@ int __init tboot_parse_dmar_table(acpi_table_handler 
> > dmar_handler)
> >       rc = dmar_handler(dmar_table);
> >       xfree(dmar_table);
> >   
> > -    /* acpi_parse_dmar() zaps APCI DMAR signature in TXT heap table */
> > -    /* but dom0 will read real table, so must zap it there too */
> > +    /* Dom0 will read real DMAR table, so must zap it there */
> >       acpi_dmar_zap();
> >   
> >       return rc;
> > --- a/xen/drivers/passthrough/vtd/dmar.c
> > +++ b/xen/drivers/passthrough/vtd/dmar.c
> > @@ -866,8 +866,10 @@ static int __init acpi_parse_dmar(struct acpi_table_header 
> > *table)
> >       }
> >   
> >   out:
> > +#ifndef CONFIG_TBOOT
> >       /* Zap ACPI DMAR signature to prevent dom0 using vt-d HW. */
> >       acpi_dmar_zap();
> > +#endif
> >       return ret;
> >   }
> >   
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