linux-kernel - Re: [PATCH 5/6] x86/hyperv: Support hypercalls for TDX guests

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Date:   Mon, 28 Nov 2022 07:22:27 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Dexuan Cui <decui@...rosoft.com>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "arnd@...db.de" <arnd@...db.de>, "bp@...en8.de" <bp@...en8.de>,
        "brijesh.singh@....com" <brijesh.singh@....com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "jane.chu@...cle.com" <jane.chu@...cle.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        KY Srinivasan <kys@...rosoft.com>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "luto@...nel.org" <luto@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "seanjc@...gle.com" <seanjc@...gle.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        "x86@...nel.org" <x86@...nel.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/6] x86/hyperv: Support hypercalls for TDX guests

On 11/27/22 16:58, Dexuan Cui wrote:
> +u64 hv_tdx_hypercall(u64 control, u64 input_addr, u64 output_addr)
> +{
> +	struct tdx_hypercall_args args = { };
> +
> +	if (!(control & HV_HYPERCALL_FAST_BIT)) {
> +		if (input_addr)
> +			input_addr += ms_hyperv.shared_gpa_boundary;
> +
> +		if (output_addr)
> +			output_addr += ms_hyperv.shared_gpa_boundary;
> +	}

This:

>
https://learn.microsoft.com/en-us/virtualization/hyper-v-on-windows/tlfs/hypercall-interface

makes it sound like HV_HYPERCALL_FAST_BIT says whether arguments go in
registers (fast) or memory (slow).  But this hv_tdx_hypercall() function
looks like it takes addresses only.

*Is* there a register based calling convention to make Hyper-V
hypercalls when running under TDX?

Also, is this the output address manipulation fundamentally different from:

	output_addr = cc_mkdec(output_addr);

?  Decrypted addresses are the shared ones, right?