linux-kernel - Re: [PATCH 1/2] mips: vdso: prefer do_mmap() to mmap

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Message-ID: <f5cuqzzcy6kqskkpuk4hcagteqvxghnj43563felem7j2nsk2h@fgrl4ctbwgpe>
Date: Thu, 2 Jan 2025 12:25:07 -0500
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-mips@...r.kernel.org
Subject: Re: [PATCH 1/2] mips: vdso: prefer do_mmap() to mmap_region()

* Lorenzo Stoakes <lorenzo.stoakes@...cle.com> [250102 07:11]:
> mmap_region() is an internal memory management implementation detail that
> is not intended to be used outside of the memory management subsystem.
> 
> Map the delay slot emulation page using do_mmap() which makes use of the
> already-held mmap write lock and bypasses unneeded populate and userfaultfd
> logic.
> 
> This should have the precise same behaviour as the existing logic.

this looks to do the same thing, but a bit heavier - which should be
fine here.

> 
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

Reviewed-by: Liam R. Howlett <Liam.Howlett@...cle.com>

> ---
>  arch/mips/kernel/vdso.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/mips/kernel/vdso.c b/arch/mips/kernel/vdso.c
> index 4c8e3c0aa210..75c9d3618f58 100644
> --- a/arch/mips/kernel/vdso.c
> +++ b/arch/mips/kernel/vdso.c
> @@ -11,6 +11,7 @@
>  #include <linux/ioport.h>
>  #include <linux/kernel.h>
>  #include <linux/mm.h>
> +#include <linux/mman.h>
>  #include <linux/random.h>
>  #include <linux/sched.h>
>  #include <linux/slab.h>
> @@ -97,11 +98,12 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
>  		return -EINTR;
>  
>  	if (IS_ENABLED(CONFIG_MIPS_FP_SUPPORT)) {
> +		unsigned long unused;
> +
>  		/* Map delay slot emulation page */
> -		base = mmap_region(NULL, STACK_TOP, PAGE_SIZE,
> -				VM_READ | VM_EXEC |
> -				VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC,
> -				0, NULL);
> +		base = do_mmap(NULL, STACK_TOP, PAGE_SIZE, PROT_READ | PROT_EXEC,
> +			       MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, 0, 0, &unused,
> +			       NULL);
>  		if (IS_ERR_VALUE(base)) {
>  			ret = base;
>  			goto out;
> -- 
> 2.47.1
>