Messages in this thread | | | Date | Thu, 22 Oct 2020 12:45:27 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] x86/alternative: don't call text_poke() in lazy TLB mode |
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On Thu, Oct 22, 2020 at 11:24:39AM +0200, Jürgen Groß wrote: > On 09.10.20 16:42, Juergen Gross wrote: > > When running in lazy TLB mode the currently active page tables might > > be the ones of a previous process, e.g. when running a kernel thread. > > > > This can be problematic in case kernel code is being modified via > > text_poke() in a kernel thread, and on another processor exit_mmap() > > is active for the process which was running on the first cpu before > > the kernel thread. > > > > As text_poke() is using a temporary address space and the former > > address space (obtained via cpu_tlbstate.loaded_mm) is restored > > afterwards, there is a race possible in case the cpu on which > > exit_mmap() is running wants to make sure there are no stale > > references to that address space on any cpu active (this e.g. is > > required when running as a Xen PV guest, where this problem has been > > observed and analyzed). > > > > In order to avoid that, drop off TLB lazy mode before switching to the > > temporary address space. > > > > Fixes: cefa929c034eb5d ("x86/mm: Introduce temporary mm structs") > > Signed-off-by: Juergen Gross <jgross@suse.com> > > Can anyone look at this, please? It is fixing a real problem which has > been seen several times.
As it happens I picked it up yesterday, just pushed it out for you.
Thanks!
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