Messages in this thread | | | Subject | Re: [PATCH] x86/alternative: don't call text_poke() in lazy TLB mode | From | Jürgen Groß <> | Date | Thu, 22 Oct 2020 12:48:40 +0200 |
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On 22.10.20 12:45, Peter Zijlstra wrote: > 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.
Thank you very much!
Juergen
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