Messages in this thread | | | Date | Mon, 18 Jul 2022 09:19:01 +0100 | From | Ken Moffat <> | Subject | Retbleed, Zen2 and STIBP |
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Probably like most people, I find the detail of the available retbleed mitigations obscure. In particular, for zen2 the options *might* include ibpb or unret.
But I have failed to find what 'unret' actually means. Any pointers, please ?
While ibpb might be available (and slow), on my Renoir with microcode level (0860106h) there were no newer microcode versions available when I last looked (a few weeks ago) but note 7 at the bottom of https://www.amd.com/system/files/documents/technical-guidance-for-mitigating-branch-type-confusion_v 7_20220712.pdf implies that the relevant bit is only set on Renoir in 0860109h and later.
Some of the text in that pdf implies that at least one of the options could be set if not already set from the microcode, but the amount of detail leaves me totally lost.
Assuming, for the moment, that I might want to try this full mitigation, is there any way to set this in the absence of newer microcode ?
Or should I just accept that the best I can get is 'unret', whatever that means ?
ĸen -- It is very easy to get ridiculously confused about the tenses of time travel, but most things can be resolved by a sufficiently large ego. -- The Last Continent
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