On 22.08.2023 16:53, Andrew Cooper wrote: > On 22/08/2023 3:22 pm, Jan Beulich wrote: >> Reportedly the AMD Custom APU 0405 found on SteamDeck, models 0x90 and >> 0x91, (quoting the respective Linux commit) is similarly affected. Put >> another instance of our Zen1 vs Zen2 distinction checks in >> amd_check_zenbleed(), forcing use of the chickenbit irrespective of >> ucode version (building upon real hardware never surfacing a version of >> 0xffffffff). >> >> Signed-off-by: Jan Beulich <[email protected]> >> >> --- a/xen/arch/x86/cpu/amd.c >> +++ b/xen/arch/x86/cpu/amd.c >> @@ -936,10 +936,14 @@ void amd_check_zenbleed(void) >> case 0xa0 ... 0xaf: good_rev = 0x08a00008; break; >> default: >> /* >> - * With the Fam17h check above, parts getting here are Zen1. >> - * They're not affected. >> + * With the Fam17h check above, most parts getting here are >> + * Zen1. They're not affected. Assume Zen2 ones making it >> + * here are affected regardless of microcode version. > > It's not really "assume Zen2 are vulnerable".
But that's also not what the comment says. It says "regardless of microcode version". > All Zen2 *are* > vulnerable, but we keep on finding new CPUs that AMD did for special > circumstances and haven't documented in their model lists. > > Furthermore, there needs to be another sentence: > > "Because we still don't have an correct authoritative list of Zen1 vs > Zen2 by model number, use STIBP as a heuristic to distinguish." > > Or something like this. It is important to state that STIBP is our > model-heuristic here. Will add. > With some kind of note explaining what's going on, Reviewed-by: Andrew > Cooper <[email protected]> Thanks. >> */ >> - return; >> + if (!boot_cpu_has(X86_FEATURE_AMD_STIBP)) >> + return; >> + good_rev = ~0u; > > While I hate to review like this, someone is going to come along and > swap this u for U for MISRA reasons. Probably best to adjust it now. Oh, right, will do. Jan
