Re: [PATCH v19 030/130] KVM: TDX: Add helper functions to print TDX SEAMCALL error

Isaku Yamahata
2024-03-20T21:52:31Z

On Wed, Mar 20, 2024 at 01:29:07PM +1300,
"Huang, Kai" <kai.huang@intel.com> wrote:

>
>
> On 26/02/2024 9:25 pm, isaku.yamahata@intel.com wrote:
> > From: Isaku Yamahata <isaku.yamahata@intel.com>
> >
> > Add helper functions to print out errors from the TDX module in a uniform
> > manner.
>
> Likely we need more information here. See below.
>
> >
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> > Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
> > Reviewed-by: Yuan Yao <yuan.yao@intel.com>
> > ---
> > v19:
> > - dropped unnecessary include <asm/tdx.h>
> >
> > v18:
> > - Added Reviewed-by Binbin.
>
> The tag doesn't show in the SoB chain.
>
> >
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> > ---
>
> [...]
>
> > +void pr_tdx_error(u64 op, u64 error_code, const struct tdx_module_args *out)
> > +{
> > + if (!out) {
> > + pr_err_ratelimited("SEAMCALL (0x%016llx) failed: 0x%016llx\n",
> > + op, error_code);
> > + return;
> > + }
>
> I think this is the reason you still want the @out in tdx_seamcall()?
>
> But I am not sure either -- even if you want to have @out *here* -- why
> cannot you pass a NULL explicitly when you *know* the concerned SEAMCALL
> doesn't have a valid output?
>
> > +
> > +#define MSG \
> > + "SEAMCALL (0x%016llx) failed: 0x%016llx RCX 0x%016llx RDX 0x%016llx R8 0x%016llx R9 0x%016llx R10 0x%016llx R11 0x%016llx\n"
> > + pr_err_ratelimited(MSG, op, error_code, out->rcx, out->rdx, out->r8,
> > + out->r9, out->r10, out->r11);
> > +}
>
> Besides the regs that you are printing, there are more regs (R12-R15, RDI,
> RSI) in the structure.
>
> It's not clear why you only print some, but not all.
>
> AFAICT the VP.ENTER SEAMCALL can have all regs as valid output?

Only those are used for SEAMCALLs except TDH.VP.ENTER. TDH.VP.ENTER is an
exception.

As discussed at [1], out can be eliminated. We will have only limited output.
If we go for that route, we'll have the two following functions.
Does it make sense?

void pr_tdx_error(u64 op, u64 error_code)
{
pr_err_ratelimited("SEAMCALL (0x%016llx) failed: 0x%016llx\n",
op, error_code);
}

void pr_tdx_sept_error(u64 op, u64 error_code, const union tdx_sept_entry *entry,
const union tdx_sept_level_state *level_state)
{
#define MSG \
"SEAMCALL (0x%016llx) failed: 0x%016llx entry 0x%016llx level_state 0x%016llx\n"
pr_err_ratelimited(MSG, op, error_code, entry->raw, level_state->raw);
}

[1] https://lore.kernel.org/kvm/20240320213600.GI1994522@ls.amr.corp.intel.com/

>
> Anyway, that being said, you might need to put more text in
> changelog/comment to make this patch (at least more) reviewable.
>

--
Isaku Yamahata <isaku.yamahata@intel.com>