On Wed, Nov 15, 2023 at 10:41:46AM +0000, "Huang, Kai" <kai.huang@xxxxxxxxx> wrote: > > > > +#include <asm/archrandom.h> > > > + > > > +typedef u64 (*sc_func_t)(u64 fn, struct tdx_module_args *args); > > > + > > > +static inline u64 sc_retry(sc_func_t func, u64 fn, > > > + struct tdx_module_args *args) > > > +{ > > > + int retry = RDRAND_RETRY_LOOPS; > > > + u64 ret; > > > + > > > + do { > > > + ret = func(fn, args); > > > + } while (ret == TDX_RND_NO_ENTROPY && --retry); > > > > This loop assumes that args isn't touched when TDX_RND_NO_ENTRYPOY is returned. > > It's not true. TDH.SYS.INIT() and TDH.SYS.LP.INIT() clear RCX, RDX, etc on > > error including TDX_RND_NO_ENTRY. Because TDH.SYS.INIT() takes RCX as input, > > this wrapper doesn't work. TDH.SYS.LP.INIT() doesn't use RCX, RDX ... as > > input. So it doesn't matter. > > > > Other SEAMCALLs doesn't touch registers on the no entropy error. > > TDH.EXPORTS.STATE.IMMUTABLE(), TDH.IMPORTS.STATE.IMMUTABLE(), TDH.MNG.ADDCX(), > > and TDX.MNG.CREATE(). TDH.SYS.INIT() is an exception. > > If I am reading the spec (TDX module 1.5 ABI) correctly the TDH.SYS.INIT doesn't > return TDX_RND_NO_ENTROPY. The next updated spec would fix it. > TDH.SYS.LP.INIT indeed can return NO_ENTROPY but as > you said it doesn't take any register as input. So technically the code works > fine. (Even the TDH.SYS.INIT can return NO_ENTROPY the code still works fine > because the RCX must be 0 for TDH.SYS.INIT.) Ah yes, I agree with you. So it doesn't matter. > Also, I can hardly think out of any reason why TDX module needs to clobber input > registers in case of NO_ENTROPY for *ANY* SEAMCALL. But despite that, I am not > opposing the idea that it *MIGHT* be better to "not assume" NO_ENTROPY will > never clobber registers either, e.g., for the sake of future extendibility. In > this case, the below diff should address: Now we agreed that TDH.SYS.INIT() and TDH.SYS.LP.INIT() doesn't matter, I'm fine with this patch. (TDX KVM handles other SEAMCALLS itself.) Reviewed-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx> -- Isaku Yamahata <isaku.yamahata@xxxxxxxxxxxxxxx>