On Wed, 2023-06-28 at 14:58 +0200, Peter Zijlstra wrote:
> On Tue, Jun 27, 2023 at 02:12:35AM +1200, Kai Huang wrote:
>
> > +static int __always_unused seamcall(u64 fn, u64 rcx, u64 rdx, u64 r8, u64 r9,
>
> __always_inline perhaps? __always_unused seems wrong, worse it's still
> there at the end of the series:
>
> $ quilt diff --combine - | grep seamcall
> ...
> +static int __always_unused seamcall(u64 fn, u64 rcx, u64 rdx, u64 r8, u64 r9,
> ...
> + ret = seamcall(TDH_SYS_INIT, 0, 0, 0, 0, NULL, NULL);
> + ret = seamcall(TDH_SYS_LP_INIT, 0, 0, 0, 0, NULL, NULL);
> + ret = seamcall(TDH_SYS_INFO, sysinfo_pa, TDSYSINFO_STRUCT_SIZE,
> + ret = seamcall(TDH_SYS_CONFIG, __pa(tdmr_pa_array),
> + return seamcall(TDH_SYS_KEY_CONFIG, 0, 0, 0, 0, NULL, NULL);
> + ret = seamcall(TDH_SYS_TDMR_INIT, tdmr->base, 0, 0, 0, NULL,
> ...
>
> Definitely not unused.
Thanks for reviewing!
Sorry obviously I forgot to remove __always_unused in the patch that firstly
used seamcall(). Should be more careful. :(
>
> > + u64 *seamcall_ret,
> > + struct tdx_module_output *out)
>
> This interface is atrocious :/ Why have these two ret values? Why can't
> that live in a single space -- /me looks throught the callers, and finds
> seamcall_ret is unused :-(
I'll @seamcall_ret as also suggested by Kirill.
>
> Worse, the input (c,d,8,9) is a strict subset of the output
> (c,d,8,9,10,11) so why isn't that a single thing used for both input and
> output.
>
> struct tdx_call {
> u64 rcx, rdx, r8, r9, r10, r11;
> };
>
> static int __always_inline seamcall(u64 fn, struct tdx_call *regs)
> {
> }
>
>
> struct tdx_regs regs = { };
> ret = seamcall(THD_SYS_INIT, ®s);
>
>
>
> struct tdx_regs regs = {
> .rcx = sysinfo_pa, .rdx = TDXSYSINFO_STRUCT_SIZE,
> .r8 = cmr_array_pa, .r9 = MAX_CMRS,
> };
> ret = seamcall(THD_SYS_INFO, ®s);
> if (ret)
> return ret;
>
> print_cmrs(cmr_array, regs.r9);
>
>
> /me looks more at this stuff and ... WTF!?!?
>
> Can someone explain to me why __tdx_hypercall() is sane (per the above)
> but then we grew __tdx_module_call() as an absolute abomination and are
> apparently using that for seam too?
>
>
Sorry I don't know the story behind __tdx_hypercall().
For TDCALL and SEAMCALL, I believe one reason is they can be used in performance
critical path. The @out is not always used, so putting all outputs to a
structure can reduce the number of function parameters. I once had separate
struct tdx_seamcall_input {} and struct tdx_seamcall_out {} but wasn't
preferred.
Kirill, could you help to explain?
>
>
> > +{
> > + u64 sret;
> > + int cpu;
> > +
> > + /* Need a stable CPU id for printing error message */
> > + cpu = get_cpu();
>
> And that's important because?
>
I want to have a stable cpu for error message printing.
> Does having preemption off across the
> seamcall make sense? Does it still make sense when you add a loop later?
SEAMCALL itself isn't interruptible, so I think having preemption off around
SEAMCALL is fine. But I agree disabling preemption around multiple SEAMCALL
isn't ideal. I'll change that to only disable preemption around one SEAMCALL to
get a correct CPU id for error printing.
>
> > + sret = __seamcall(fn, rcx, rdx, r8, r9, out);
> > + put_cpu();
> > +
> > + /* Save SEAMCALL return code if the caller wants it */
> > + if (seamcall_ret)
> > + *seamcall_ret = sret;
> > +
> > + switch (sret) {
> > + case 0:
> > + /* SEAMCALL was successful */
> > + return 0;
> > + case TDX_SEAMCALL_VMFAILINVALID:
> > + pr_err_once("module is not loaded.\n");
> > + return -ENODEV;
> > + default:
> > + pr_err_once("SEAMCALL failed: CPU %d: leaf %llu, error 0x%llx.\n",
> > + cpu, fn, sret);
> > + if (out)
> > + pr_err_once("additional output: rcx 0x%llx, rdx 0x%llx, r8 0x%llx, r9 0x%llx, r10 0x%llx, r11 0x%llx.\n",
> > + out->rcx, out->rdx, out->r8,
> > + out->r9, out->r10, out->r11);
>
> At the very least this lacks { }, but it is quite horrendous coding
> style.
>
> Why switch() at all, would not:
>
> if (!rset)
> return 0;
>
> if (sret == TDX_SEAMCALL_VMFAILINVALID) {
> pr_nonsense();
> return -ENODEV;
> }
>
> if (sret == TDX_SEAMCALL_GP) {
> pr_nonsense();
> return -ENODEV;
> }
>
> if (sret == TDX_SEAMCALL_UD) {
> pr_nonsense();
> return -EINVAL;
> }
>
> pr_nonsense();
> return -EIO;
>
> be much clearer and have less horrific indenting issues?
I can certainly change to this style. Thanks.
