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Message-ID: <SA1PR21MB1335BA9D27891F6B1BA3A988BF139@SA1PR21MB1335.namprd21.prod.outlook.com>
Date: Mon, 28 Nov 2022 19:03:37 +0000
From: Dexuan Cui <decui@...rosoft.com>
To: Dave Hansen <dave.hansen@...el.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
> From: Dave Hansen <dave.hansen@...el.com>
> Sent: Monday, November 28, 2022 7:22 AM
> [...]
> 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:
> [...]
> 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.
Good point! When hv_tdx_hypercall() is called from hv_do_fast_hypercall8()
and hv_do_fast_hypercall16(), actually the two parameters are not memory
addresses. I'll rename the parameters to param1 and param2.
I also realized I need to export the function for drivers.
> *Is* there a register based calling convention to make Hyper-V
> hypercalls when running under TDX?
When hv_tdx_hypercall() is called from hv_do_fast_hypercall8()
and hv_do_fast_hypercall16(), the params are indeed passed via registers
rather than memory.
> Also, is this the output address manipulation fundamentally different from:
>
> output_addr = cc_mkdec(output_addr);
>
> ? Decrypted addresses are the shared ones, right?
Yes.
Good point -- I'll use the updated version:
u64 hv_tdx_hypercall(u64 control, u64 param1, u64 param2)
{
struct tdx_hypercall_args args = { };
if (!(control & HV_HYPERCALL_FAST_BIT)) {
if (param1)
param1 = cc_mkdec(param1);
if (param2)
param2 = cc_mkdec(param2);
}
args.r10 = control;
args.rdx = param1;
args.r8 = param2;
(void)__tdx_hypercall(&args, TDX_HCALL_HAS_OUTPUT);
return args.r11;
}
EXPORT_SYMBOL_GPL(hv_tdx_hypercall);
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