Messages in this thread | | | From | "Jason A. Donenfeld" <> | Date | Wed, 25 May 2022 22:36:15 +0200 | Subject | Re: [patch 0/3] x86/fpu: Prevent FPU state corruption |
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Hey folks,
An update on the VirtualBox thing (not that anybody here actually cares, but at least I've been nerd sniped):
It looks like they've got a patch out now for it: https://www.virtualbox.org/attachment/ticket/20914/vbox-linux-5.18.patch It seems like they call kernel_fpu_begin() before loading guest fpu regs, but then immediately re-enable preemption. Yikes. So if another kernel task preempts that one and uses the fpu... And it makes me wonder the extent of this breakage prior (maybe not just hardirq? unsure.). Also, it apparently is only enabled for 5.18, so that doesn't help with old kernels. Oh well. All that development happens behind closed doors so probably not worth losing sleep over.
Anyway, from a kernel perspective, there's now no urgency for us to do anything about this. VirtualBox won't compile for 5.18 without that patch, and given that Oracle fixed it, it doesn't appear to be our bug. Case closed. So if we go ahead with removing hardirq fpu support, it won't be due to this but for other motivations.
Jason
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