linux-kernel - Re: [PATCH 19/26] percpu: clean up all mappings when pcpu_map

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Message-ID: <CAJD7tkahJ3NzBgvB0CwsNUce3a-Gg_GzcYRMy6GsLONcudnJYA@mail.gmail.com>
Date: Mon, 15 Jul 2024 18:33:59 -0700
From: Yosry Ahmed <yosryahmed@...gle.com>
To: Brendan Jackman <jackmanb@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>, 
	Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
	Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	Alexandre Chartre <alexandre.chartre@...cle.com>, Liran Alon <liran.alon@...cle.com>, 
	Jan Setje-Eilers <jan.setjeeilers@...cle.com>, Catalin Marinas <catalin.marinas@....com>, 
	Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Mel Gorman <mgorman@...e.de>, 
	Lorenzo Stoakes <lstoakes@...il.com>, David Hildenbrand <david@...hat.com>, Vlastimil Babka <vbabka@...e.cz>, 
	Michal Hocko <mhocko@...nel.org>, Khalid Aziz <khalid.aziz@...cle.com>, 
	Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>, 
	Dietmar Eggemann <dietmar.eggemann@....com>, Steven Rostedt <rostedt@...dmis.org>, 
	Valentin Schneider <vschneid@...hat.com>, Paul Turner <pjt@...gle.com>, Reiji Watanabe <reijiw@...gle.com>, 
	Junaid Shahid <junaids@...gle.com>, Ofir Weisse <oweisse@...gle.com>, 
	Patrick Bellasi <derkling@...gle.com>, KP Singh <kpsingh@...gle.com>, 
	Alexandra Sandulescu <aesa@...gle.com>, Matteo Rizzo <matteorizzo@...gle.com>, Jann Horn <jannh@...gle.com>, 
	x86@...nel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	kvm@...r.kernel.org, Dennis Zhou <dennis@...nel.org>
Subject: Re: [PATCH 19/26] percpu: clean up all mappings when pcpu_map_pages() fails

On Fri, Jul 12, 2024 at 10:01 AM Brendan Jackman <jackmanb@...gle.com> wrote:
>
> From: Yosry Ahmed <yosryahmed@...gle.com>
>
> In pcpu_map_pages(), if __pcpu_map_pages() fails on a CPU, we call
> __pcpu_unmap_pages() to clean up mappings on all CPUs where mappings
> were created, but not on the CPU where __pcpu_map_pages() fails.
>
> __pcpu_map_pages() and __pcpu_unmap_pages() are wrappers around
> vmap_pages_range_noflush() and vunmap_range_noflush(). All other callers
> of vmap_pages_range_noflush() call vunmap_range_noflush() when mapping
> fails, except pcpu_map_pages(). The reason could be that partial
> mappings may be left behind from a failed mapping attempt.
>
> Call __pcpu_unmap_pages() for the failed CPU as well in
> pcpu_map_pages().
>
> This was found by code inspection, no failures or bugs were observed.
>
> Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>
> Acked-by: Dennis Zhou <dennis@...nel.org>
>
> (am from https://lore.kernel.org/lkml/20240311194346.2291333-1-yosryahmed@google.com/)

This went into v6.10 as commit 2ccd48ce35e87f09472b42dda96fbf7b5165f3c3.

> ---
>  mm/percpu-vm.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/percpu-vm.c b/mm/percpu-vm.c
> index 2054c9213c43..cd69caf6aa8d 100644
> --- a/mm/percpu-vm.c
> +++ b/mm/percpu-vm.c
> @@ -231,10 +231,10 @@ static int pcpu_map_pages(struct pcpu_chunk *chunk,
>         return 0;
>  err:
>         for_each_possible_cpu(tcpu) {
> -               if (tcpu == cpu)
> -                       break;
>                 __pcpu_unmap_pages(pcpu_chunk_addr(chunk, tcpu, page_start),
>                                    page_end - page_start);
> +               if (tcpu == cpu)
> +                       break;
>         }
>         pcpu_post_unmap_tlb_flush(chunk, page_start, page_end);
>         return err;
>
> --
> 2.45.2.993.g49e7a77208-goog
>