Re: [PATCH v2 5/5] x86/mm: Drop usage of __flush_tlb_all() in kernel_physical_mapping_init()

[Sasha Levin]

On Fri, Nov 30, 2018 at 04:35:32PM -0800, Dan Williams wrote:
> Commit f77084d96355 "x86/mm/pat: Disable preemption around
> __flush_tlb_all()" addressed a case where __flush_tlb_all() is called
> without preemption being disabled. It also left a warning to catch other
> cases where preemption is not disabled. That warning triggers for the
> memory hotplug path which is also used for persistent memory enabling:
>
> WARNING: CPU: 35 PID: 911 at ./arch/x86/include/asm/tlbflush.h:460
> RIP: 0010:__flush_tlb_all+0x1b/0x3a
> [..]
> Call Trace:
>  phys_pud_init+0x29c/0x2bb
>  kernel_physical_mapping_init+0xfc/0x219
>  init_memory_mapping+0x1a5/0x3b0
>  arch_add_memory+0x2c/0x50
>  devm_memremap_pages+0x3aa/0x610
>  pmem_attach_disk+0x585/0x700 [nd_pmem]
>
> Andy wondered why a path that can sleep was using __flush_tlb_all() [1]
> and Dave confirmed the expectation for TLB flush is for modifying /
> invalidating existing pte entries, but not initial population [2]. Drop
> the usage of __flush_tlb_all() in phys_{p4d,pud,pmd}_init() on the
> expectation that this path is only ever populating empty entries for the
> linear map. Note, at linear map teardown time there is a call to the
> all-cpu flush_tlb_all() to invalidate the removed mappings.
>
> [1]: https://lore.kernel.org/lkml/9DFD717D-857D-493D-A606-B635D72BAC21@xxxxxxxxxxxxxx
> [2]: https://lore.kernel.org/lkml/749919a4-cdb1-48a3-adb4-adb81a5fa0b5@xxxxxxxxx
>
> Fixes: f77084d96355 ("x86/mm/pat: Disable preemption around __flush_tlb_all()")
> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Reported-by: Andy Lutomirski <luto@xxxxxxxxxx>
> Suggested-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>

Hi Dan,

This patch on it's own doesn't apply to any of the stable trees, does it
maybe depend on some of the previous patches in this series?

--
Thanks,
Sasha