tdx: Document tdx failure_inject sysfs parameters

Add documentation for the sysfs parameters for the TDX tdcall
failure/random failure injection

Signed-off-by: Andi Kleen <[email protected]>

Author: Andi Kleen

Documentation/fault-injection/fault-injection.rst

@@ -52,6 +52,10 @@ Available fault injection capabilities
   status code is NVME_SC_INVALID_OPCODE with no retry. The status code and
   retry flag can be set via the debugfs.
 
+- fail_tdx
+
+  inject errors and flipped bits into Intel TDX TDCALL responses.
+
 
 Configure fault-injection capabilities behavior
 -----------------------------------------------
@@ -195,6 +199,25 @@ configuration of fault-injection capabilities.
 	use a negative errno, you better use 'printf' instead of 'echo', e.g.:
 	$ printf %#x -12 > retval
 
+- /sys/kernel/debug/fail_tdx/tdcall
+
+	enable flipping bits in TDX TDCALL responses
+
+- /sys/kernel/debug/fail_tdx/tderrors
+
+	enable injecting errors in TDX TDCALL responses
+
+- /sys/kernel/debug/fail_tdx/seed
+
+	set seed for random generator used for flipping bits in TDX TDCALL
+	responses. Note that each CPU has its own independent random generator.
+
+- /sys/kernel/debug/fail_tdx/num_change_bits
+
+	number of bits to change with tdcall=1 in TDX TDCALL responses.
+	when set to 64 the whole value is replaced with a randon number.
+	otherwise the number of bits specified are randomly flipped.
+
 Boot option
 ^^^^^^^^^^^
 
@@ -208,6 +231,8 @@ use the boot option::
 	fail_futex=
 	mmc_core.fail_request=<interval>,<probability>,<space>,<times>
 
+        fail_tdx= [seed:N,][tdcall:1,][tderrors:1,][numbits:XX],<interval>,<probability>,<space>,<times>
+
 proc entries
 ^^^^^^^^^^^^