linux-kernel - Re: [PATCH v25 19/30] mm: Update can_follow_write

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Message-ID: <20210423102522.5djgt2fb3unsidnw@box.shutemov.name>
Date:   Fri, 23 Apr 2021 13:25:22 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Cc:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        Pengfei Xu <pengfei.xu@...el.com>,
        Haitao Huang <haitao.huang@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v25 19/30] mm: Update can_follow_write_pte() for shadow
 stack

On Thu, Apr 15, 2021 at 03:14:08PM -0700, Yu-cheng Yu wrote:
> Can_follow_write_pte() ensures a read-only page is COWed by checking the
> FOLL_COW flag, and uses pte_dirty() to validate the flag is still valid.
> 
> Like a writable data page, a shadow stack page is writable, and becomes
> read-only during copy-on-write, but it is always dirty.  Thus, in the
> can_follow_write_pte() check, it belongs to the writable page case and
> should be excluded from the read-only page pte_dirty() check.  Apply
> the same changes to can_follow_write_pmd().
> 
> While at it, also split the long line into smaller ones.
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
> v25:
> - Split long line into smaller ones.
> v24:
> - Change arch_shadow_stack_mapping() to is_shadow_stack_mapping().
> 
>  mm/gup.c         | 16 ++++++++++++----
>  mm/huge_memory.c | 16 ++++++++++++----
>  2 files changed, 24 insertions(+), 8 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index ef7d2da9f03f..f2813cf4d07b 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -356,10 +356,18 @@ static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
>   * FOLL_FORCE can write to even unwritable pte's, but only
>   * after we've gone through a COW cycle and they are dirty.
>   */
> -static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
> +static inline bool can_follow_write_pte(pte_t pte, unsigned int flags,
> +					vm_flags_t vm_flags)
>  {

It might be cleaner to pass down vma pointer and dereference it within the
function: can_follow_write_pte(vma, pte, gup_flags).

Otherwise looks good to me:

Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

-- 
 Kirill A. Shutemov