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

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Message-ID: <e79c4b97-5718-9a60-406f-1df994ba089c@linux.intel.com>
Date:   Fri, 9 Dec 2022 07:42:56 -0800
From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>
Cc:     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 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.

> +}
> +
>  static void tdx_parse_tdinfo(u64 *cc_mask)
>  {
>  	struct tdx_module_output out;
> @@ -172,7 +208,7 @@ static void tdx_parse_tdinfo(u64 *cc_mask)
>  	 */
>  	td_attr = out.rdx;
>  	if (!(td_attr & ATTR_SEPT_VE_DISABLE))
> -		panic("TD misconfiguration: SEPT_VE_DISABLE attibute must be set.\n");
> +		tdx_panic("TD misconfiguration: SEPT_VE_DISABLE attribute must be set.");
>  }
>  
>  /*

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer