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

Kirill A. Shutemov
2022-12-09T17:08:16Z

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@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.

Hm. What difference would it make?

--
Kiryl Shutsemau / Kirill A. Shutemov