linux-kernel - Re: [PATCH v5 17/26] hugetlb/userfaultfd: Hook page faults for uffd write protection

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Date:   Wed, 21 Jul 2021 17:50:11 -0400
From:   Peter Xu <peterx@...hat.com>
To:     kernel test robot <lkp@...el.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        clang-built-linux@...glegroups.com, kbuild-all@...ts.01.org,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Jerome Glisse <jglisse@...hat.com>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Alistair Popple <apopple@...dia.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v5 17/26] hugetlb/userfaultfd: Hook page faults for uffd
 write protection

On Tue, Jul 20, 2021 at 11:37:36PM +0800, kernel test robot wrote:
> config: s390-randconfig-r023-20210716 (attached as .config)

[...]

> >> mm/hugetlb.c:5063:29: error: implicit declaration of function 'huge_pte_uffd_wp' [-Werror,-Wimplicit-function-declaration]
>            if (userfaultfd_wp(vma) && huge_pte_uffd_wp(huge_ptep_get(ptep)) &&
>                                       ^
>    12 warnings and 1 error generated.

I remember I raised this question once on why s390 redefines a lot of huge pte
operations on its own even if they're defined the same in generic hugetlb.h..
I think there was a plan to rework that but definitely not landed yet.

Will sqaush below into the patch "mm/hugetlb: Introduce huge pte version of
uffd-wp helpers":

---8<---
diff --git a/arch/s390/include/asm/hugetlb.h b/arch/s390/include/asm/hugetlb.h
index 60f9241e5e4a..19c4b4431d27 100644
--- a/arch/s390/include/asm/hugetlb.h
+++ b/arch/s390/include/asm/hugetlb.h
@@ -115,6 +115,21 @@ static inline pte_t huge_pte_modify(pte_t pte, pgprot_t newprot)
        return pte_modify(pte, newprot);
 }
 
+static inline pte_t huge_pte_mkuffd_wp(pte_t pte)
+{
+       return pte;
+}
+
+static inline pte_t huge_pte_clear_uffd_wp(pte_t pte)
+{
+       return pte;
+}
+
+static inline int huge_pte_uffd_wp(pte_t pte)
+{
+       return 0;
+}
+
 static inline bool gigantic_page_runtime_supported(void)
 {
        return true;
---8<---

Thanks,

-- 
Peter Xu