On Thu, 2023-03-23 at 06:49 -0700, Hansen, Dave wrote:
> On 3/15/23 04:10, Huang, Kai wrote:
> > I can do. Just want to make sure do you want to retry TDX_SYS_BUSY, or retry
> > TDX_RND_NO_ENTROPY (if we want to ask TDX module guys to change to return this
> > value)?
>
> I'll put it this way:
>
> Linux is going to treat TDX_SYS_BUSY like a Linux bug and assume
> Linux is doing something wrong. It'll mostly mean that
> users will see something nasty and may even cause Linux to give
> up on TDX. In other words, the TDX module shouldn't use
> TDX_SYS_BUSY for things that aren't Linux's fault.
>
> > Also, even we retry either TDX_SYS_BUSY or TDX_RND_NO_ENTROPY in common
> > seamcall() code, it doesn't handle the TDH.SYS.KEY.CONFIG, because sadly this
> > SEAMCALL returns a different error code:
> >
> > TDX_KEY_GENERATION_FAILED Failed to generate a random key. This is
> > typically caused by an entropy error of the
> > CPU's random number generator, and may
> > be impacted by RDSEED, RDRAND or PCONFIG
> > executing on other LPs. The operation should be
> > retried.
>
> Sounds like we should just replace TDX_KEY_GENERATION_FAILED with
> TDX_RND_NO_ENTROPY in cases where key generation fails because of a lack
> of entropy.
Thanks for feedback.
I'll do following, please let me know for any comments in case I have any
misunderstanding.
1) In TDH.SYS.INIT, ask TDX module team to return TDX_RND_NO_ENTROPY instead of
TDX_SYS_BUSY when running out of entropy.
2) In TDH.SYS.KEY.CONFIG, ask TDX module to return TDX_RND_NO_ENTROPY instead of
TDX_KEY_GENERATION_FAILED when running out of entropy. Whether
TDX_KEY_GENERATION_FAILED should be still kept is up to TDX module team
(because it looks running concurrent PCONFIGs is also related).
3) Ask TDX module to always return TDX_RND_NO_ENTROPY in _ALL_ SEAMCALLs and
keep this behaviour for future TDX modules too.
4) In the common seamcall(), retry on TDX_RND_NO_ENTROPY.
In terms of how many times to retry, I will use a fixed value for now, similar
to the kernel code below:
#define RDRAND_RETRY_LOOPS 10
/* Unconditional execution of RDRAND and RDSEED */
static inline bool __must_check rdrand_long(unsigned long *v)
{
bool ok;
unsigned int retry = RDRAND_RETRY_LOOPS;
do {
asm volatile("rdrand %[out]"
CC_SET(c)
: CC_OUT(c) (ok), [out] "=r" (*v));
if (ok)
return true;
} while (--retry);
return false;
}
