linux-kernel - Re: [PATCH 2/4] x86/tdx: Use ReportFatalError to report missing SEPT_VE

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Date:   Fri, 9 Dec 2022 20:06:47 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Elena Reshetova <elena.reshetova@...el.com>, x86@...nel.org,
        linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] x86/tdx: Use ReportFatalError to report missing
 SEPT_VE_DISABLE

On Fri, Dec 09, 2022 at 07:42:56AM -0800, Sathyanarayanan Kuppuswamy wrote:
> 
> 
> On 12/9/22 5:25 AM, Kirill A. Shutemov wrote:
> > The check for SEPT_VE_DISABLE happens early in the kernel boot where
> > earlyprintk is not yet functional. Kernel successfully detect broken
> > TD configuration and stops the kernel with panic(), but it cannot
> > communicate the reason to the user.
> > 
> > Use TDG.VP.VMCALL<ReportFatalError> to report the error. The hypercall
> > can encode message up to 64 bytes in eight registers.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > ---
> >  arch/x86/coco/tdx/tdx.c | 38 +++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 37 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
> > index cfd4c95b9f04..8ad04d101270 100644
> > --- a/arch/x86/coco/tdx/tdx.c
> > +++ b/arch/x86/coco/tdx/tdx.c
> > @@ -22,6 +22,7 @@
> >  
> >  /* TDX hypercall Leaf IDs */
> >  #define TDVMCALL_MAP_GPA		0x10001
> > +#define TDVMCALL_REPORT_FATAL_ERROR	0x10003
> >  
> >  /* MMIO direction */
> >  #define EPT_READ	0
> > @@ -140,6 +141,41 @@ int tdx_mcall_get_report0(u8 *reportdata, u8 *tdreport)
> >  }
> >  EXPORT_SYMBOL_GPL(tdx_mcall_get_report0);
> >  
> > +static void __noreturn tdx_panic(const char *msg)
> > +{
> > +	struct tdx_hypercall_args args = {
> > +		.r10 = TDX_HYPERCALL_STANDARD,
> > +		.r11 = TDVMCALL_REPORT_FATAL_ERROR,
> > +		.r12 = 0, /* Error code: 0 is Panic */
> > +	};
> > +	union {
> > +		/* Define register order according to the GHCI */
> > +		struct { u64 r14, r15, rbx, rdi, rsi, r8, r9, rdx; };
> > +
> > +		char str[64];
> > +	} message;
> > +
> > +	/* VMM assumes '\0' in byte 65, if the message took all 64 bytes */
> > +	strncpy(message.str, msg, 64);
> > +
> > +	args.r8  = message.r8;
> > +	args.r9  = message.r9;
> > +	args.r14 = message.r14;
> > +	args.r15 = message.r15;
> > +	args.rdi = message.rdi;
> > +	args.rsi = message.rsi;
> > +	args.rbx = message.rbx;
> > +	args.rdx = message.rdx;
> > +
> > +	/*
> > +	 * Keep calling the hypercall in case VMM did not terminated
> > +	 * the TD as it must.
> > +	 */
> > +	while (1) {
> > +		__tdx_hypercall(&args, 0);
> > +	}
> 
> Instead of an infinite loop, I'm wondering if the guest should panic after
> retrying for few times.

Hm. What difference would it make?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov