Re: [PATCH 2/4] x86/tdx: Use ReportFatalError to report missing SEPT_VE_DISABLE

Sathyanarayanan Kuppuswamy
2022-12-09T15:43:08Z

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@linux.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