Messages in this thread | | | Subject | Re: [PATCH] KVM: nSVM: prepare guest save area while is_guest_mode is true | From | Paolo Bonzini <> | Date | Thu, 18 Feb 2021 19:00:40 +0100 |
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On 18/02/21 18:42, Sean Christopherson wrote: >> The bug is present since commit 06fc7772690d ("KVM: SVM: Activate nested >> state only when guest state is complete", 2010-04-25). Unfortunately, >> it is not clear from the commit message what issue exactly led to the >> change back then. It was probably related to svm_set_cr0 however because >> the patch series cover letter[1] mentioned lazy FPU switching. > > Aha! It was indeed related to svm_set_cr0(). Specifically, the next patch, > commit 66a562f7e257 ("KVM: SVM: Make lazy FPU switching work with nested svm"), > added is_nested() checks in update_cr0_intercept() to merge L1's intercepts with > L0's intercepts.
Yeah, the problem is I don't understand why 06fc7772690d fixed things in 11 year old KVM instead of breaking them, because effectively this patch is reverting it.
I don't care _that_ much because so much has changed since then; the world switch logic is abstracted better nowadays, and it is easier to review the change. But it is weird, nevertheless.
Paolo
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