Re: [PATCH v5 06/12] x86/tdx: Get TD execution environment information via TDINFO

[Kuppuswamy, Sathyanarayanan]

On 8/20/21 10:13 AM, Borislav Petkov wrote:
> On Wed, Aug 04, 2021 at 11:13:23AM -0700, Kuppuswamy Sathyanarayanan wrote:
> > From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> >
> > Per Guest-Host-Communication Interface (GHCI) for Intel Trust
> > Domain Extensions (Intel TDX) specification, sec 2.4.2,
> > TDCALL[TDINFO] provides basic TD execution environment information, not
> > provided by CPUID.
> >
> > Call TDINFO during early boot to be used for following system
> > initialization.
> >
> > The call provides info on which bit in pfn is used to indicate that the
> > page is shared with the host and attributes of the TD, such as debug.
> >
> > Information about the number of CPUs need not be saved because there are
> > no users so far for it.
> >
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > Reviewed-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> > Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
> > Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
> > ---
> >
> > Changes since v4:
> >   * None
> >
> > Changes since v3:
> >   * None
> >
> >   arch/x86/kernel/tdx.c | 23 +++++++++++++++++++++++
> >   1 file changed, 23 insertions(+)
> >
> > diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
> > index 287564990f21..3973e81751ba 100644
> > --- a/arch/x86/kernel/tdx.c
> > +++ b/arch/x86/kernel/tdx.c
> > @@ -8,6 +8,14 @@
> >   
> >   #include <asm/tdx.h>
> >   
> > +/* TDX Module call Leaf IDs */
> > +#define TDINFO				1
> > +
> > +static struct {
> > +	unsigned int gpa_width;
> > +	unsigned long attributes;
> > +} td_info __ro_after_init;
>
> Where is that thing even used? I don't see it in the whole patchset.

It is used in different patch set. If you prefer to move it there, I can
move it to that patch set.

patch: https://lore.kernel.org/patchwork/patch/1472343/
series: https://lore.kernel.org/patchwork/project/lkml/list/?series=510836


> > +
> >   /*
> >    * Wrapper for standard use of __tdx_hypercall with BUG_ON() check
> >    * for TDCALL error.
> > @@ -54,6 +62,19 @@ bool tdx_prot_guest_has(unsigned long flag)
> >   }
> >   EXPORT_SYMBOL_GPL(tdx_prot_guest_has);
> >   
> > +static void tdg_get_info(void)
>
> Also, what Sean said: "tdx_" please. Unless there's a real reason to
> have a different prefix - then state that reason.
>
> > +{
> > +	u64 ret;
> > +	struct tdx_module_output out = {0};
>
> The tip-tree preferred ordering of variable declarations at the
> beginning of a function is reverse fir tree order::
>
> 	struct long_struct_name *descriptive_name;
> 	unsigned long foo, bar;
> 	unsigned int tmp;
> 	int ret;
>
> The above is faster to parse than the reverse ordering::
>
> 	int ret;
> 	unsigned int tmp;
> 	unsigned long foo, bar;
> 	struct long_struct_name *descriptive_name;
>
> And even more so than random ordering::
>
> 	unsigned long foo, bar;
> 	int ret;
> 	struct long_struct_name *descriptive_name;
> 	unsigned int tmp;

I will re-check the TDX patchset and fix the ordering issues.

> > +
> > +	ret = __tdx_module_call(TDINFO, 0, 0, 0, 0, &out);
> > +
> > +	BUG_ON(ret);
>
> WARNING: Avoid crashing the kernel - try using WARN_ON & recovery code rather than BUG() or BUG_ON()
> #121: FILE: arch/x86/kernel/tdx.c:72:
> +	BUG_ON(ret);

I have already fixed reasonable check-patch issues. For this case, we
want to use BUG_ON(). Failure in tdx_module_call means buggy TDX
module. So it is safer to crash the kernel.

> Have I already told you about checkpatch?
>
> If not, here it is:
>
> Please integrate scripts/checkpatch.pl into your patch creation
> workflow. Some of the warnings/errors *actually* make sense.

--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer