linux-kernel - Re: [PATCH v12 05/22] x86/virt/tdx: Add SEAMCALL infrastructure

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Date:   Wed, 28 Jun 2023 14:58:13 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kai Huang <kai.huang@...el.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org, dave.hansen@...el.com,
        kirill.shutemov@...ux.intel.com, tony.luck@...el.com,
        tglx@...utronix.de, bp@...en8.de, mingo@...hat.com, hpa@...or.com,
        seanjc@...gle.com, pbonzini@...hat.com, david@...hat.com,
        dan.j.williams@...el.com, rafael.j.wysocki@...el.com,
        ashok.raj@...el.com, reinette.chatre@...el.com,
        len.brown@...el.com, ak@...ux.intel.com, isaku.yamahata@...el.com,
        ying.huang@...el.com, chao.gao@...el.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, nik.borisov@...e.com,
        bagasdotme@...il.com, sagis@...gle.com, imammedo@...hat.com
Subject: Re: [PATCH v12 05/22] x86/virt/tdx: Add SEAMCALL infrastructure

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.

> +				    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 :-(

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, &regs);



	struct tdx_regs regs = {
		.rcx = sysinfo_pa,	.rdx = TDXSYSINFO_STRUCT_SIZE,
		.r8  = cmr_array_pa,	.r9  = MAX_CMRS,
	};
	ret = seamcall(THD_SYS_INFO, &regs);
	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?




> +{
> +	u64 sret;
> +	int cpu;
> +
> +	/* Need a stable CPU id for printing error message */
> +	cpu = get_cpu();

And that's important because? Does having preemption off across the
seamcall make sense? Does it still make sense when you add a loop later?

> +	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?

> +		return -EIO;
> +	}
> +}