linux-kernel - Re: [PATCH v28 16/32] x86/mm: Update maybe

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Message-ID: <YRqaesuEy9ZGttZ6@zn.tnic>
Date:   Mon, 16 Aug 2021 19:03:54 +0200
From:   Borislav Petkov <bp@...en8.de>
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>,
        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>,
        Rick P Edgecombe <rick.p.edgecombe@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v28 16/32] x86/mm: Update maybe_mkwrite() for shadow stack

On Thu, Jul 22, 2021 at 01:52:03PM -0700, Yu-cheng Yu wrote:
> diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
> index 3364fe62b903..ba449d12ec32 100644
> --- a/arch/x86/mm/pgtable.c
> +++ b/arch/x86/mm/pgtable.c
> @@ -610,6 +610,26 @@ int pmdp_clear_flush_young(struct vm_area_struct *vma,
>  }
>  #endif
>  
> +pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
> +{
> +	if (likely(vma->vm_flags & VM_WRITE))
> +		pte = pte_mkwrite(pte);
> +	else if (likely(vma->vm_flags & VM_SHADOW_STACK))
> +		pte = pte_mkwrite_shstk(pte);
> +	return pte;
> +}
> +
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
> +{
> +	if (likely(vma->vm_flags & VM_WRITE))
> +		pmd = pmd_mkwrite(pmd);
> +	else if (likely(vma->vm_flags & VM_SHADOW_STACK))
> +		pmd = pmd_mkwrite_shstk(pmd);

What are all those likely()ies here for?

-- 
Regards/Gruss,
    Boris.

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