Messages in this thread | | | Date | Thu, 8 Mar 2018 09:08:47 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 1/2] mm/vmalloc: Add interfaces to free unused page table |
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* Toshi Kani <toshi.kani@hpe.com> wrote:
> On architectures with CONFIG_HAVE_ARCH_HUGE_VMAP set, ioremap() > may create pud/pmd mappings. Kernel panic was observed on arm64 > systems with Cortex-A75 in the following steps as described by > Hanjun Guo. > > 1. ioremap a 4K size, valid page table will build, > 2. iounmap it, pte0 will set to 0; > 3. ioremap the same address with 2M size, pgd/pmd is unchanged, > then set the a new value for pmd; > 4. pte0 is leaked; > 5. CPU may meet exception because the old pmd is still in TLB, > which will lead to kernel panic. > > This panic is not reproducible on x86. INVLPG, called from iounmap, > purges all levels of entries associated with purged address on x86.
Where does x86 iounmap() do that?
> x86 still has memory leak. > Add two interfaces, pud_free_pmd_page() and pmd_free_pte_page(), > which clear a given pud/pmd entry and free up a page for the lower > level entries. > > This patch implements their stub functions on x86 and arm64, which > work as workaround.
At minimum the ordering of the patches is very confusing: why don't you introduce the new methods in patch #1, and then use them in patch #2?
Also please double check the coding style of your patches, there's a number of obvious problems of outright bad patterns and also cases where you clearly don't try to follow the (correct) style of existing code.
Thanks,
Ingo
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