linux-kernel - Re: [PATCH v2 29/37] powerpc/nohash: Replace pte_user() by pte

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Message-ID: <877cn39jyp.fsf@linux.ibm.com>
Date:   Tue, 31 Oct 2023 15:45:10 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2 29/37] powerpc/nohash: Replace pte_user() by pte_read()

Christophe Leroy <christophe.leroy@...roup.eu> writes:

> pte_user() is now only used in pte_access_permitted() to check
> access on vmas. User flag is cleared to make a page unreadable.
>
> So rename it pte_read() and remove pte_user() which isn't used
> anymore.
>
> For the time being it checks _PAGE_USER but in the near futur
> all plateforms will be converted to _PAGE_READ so lets support
> both for now.
>
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>  arch/powerpc/include/asm/nohash/32/pte-8xx.h |  7 -------
>  arch/powerpc/include/asm/nohash/pgtable.h    | 13 +++++++------
>  arch/powerpc/mm/ioremap.c                    |  4 ----
>  3 files changed, 7 insertions(+), 17 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/nohash/32/pte-8xx.h b/arch/powerpc/include/asm/nohash/32/pte-8xx.h
> index 62c965a4511a..1ee38befd29a 100644
> --- a/arch/powerpc/include/asm/nohash/32/pte-8xx.h
> +++ b/arch/powerpc/include/asm/nohash/32/pte-8xx.h
> @@ -112,13 +112,6 @@ static inline pte_t pte_mkwrite_novma(pte_t pte)
>  
>  #define pte_mkwrite_novma pte_mkwrite_novma
>  
> -static inline bool pte_user(pte_t pte)
> -{
> -	return !(pte_val(pte) & _PAGE_SH);
> -}
> -
> -#define pte_user pte_user
> -
>  static inline pte_t pte_mkhuge(pte_t pte)
>  {
>  	return __pte(pte_val(pte) | _PAGE_SPS | _PAGE_HUGE);
> diff --git a/arch/powerpc/include/asm/nohash/pgtable.h b/arch/powerpc/include/asm/nohash/pgtable.h
> index ee677162f9e6..aba56fe3b1c6 100644
> --- a/arch/powerpc/include/asm/nohash/pgtable.h
> +++ b/arch/powerpc/include/asm/nohash/pgtable.h
> @@ -160,9 +160,6 @@ static inline int pte_write(pte_t pte)
>  	return pte_val(pte) & _PAGE_WRITE;
>  }
>  #endif
> -#ifndef pte_read
> -static inline int pte_read(pte_t pte)		{ return 1; }
> -#endif
>  static inline int pte_dirty(pte_t pte)		{ return pte_val(pte) & _PAGE_DIRTY; }
>  static inline int pte_special(pte_t pte)	{ return pte_val(pte) & _PAGE_SPECIAL; }
>  static inline int pte_none(pte_t pte)		{ return (pte_val(pte) & ~_PTE_NONE_MASK) == 0; }
> @@ -190,10 +187,14 @@ static inline int pte_young(pte_t pte)
>   * and PTE_64BIT, PAGE_KERNEL_X contains _PAGE_BAP_SR which is also in
>   * _PAGE_USER.  Need to explicitly match _PAGE_BAP_UR bit in that case too.
>   */
> -#ifndef pte_user
> -static inline bool pte_user(pte_t pte)
> +#ifndef pte_read
> +static inline bool pte_read(pte_t pte)
>  {
> +#ifdef _PAGE_READ
> +	return (pte_val(pte) & _PAGE_READ) == _PAGE_READ;
> +#else
>  	return (pte_val(pte) & _PAGE_USER) == _PAGE_USER;
> +#endif
>  }
>  #endif
>  
> @@ -208,7 +209,7 @@ static inline bool pte_access_permitted(pte_t pte, bool write)
>  	 * A read-only access is controlled by _PAGE_USER bit.
>  	 * We have _PAGE_READ set for WRITE and EXECUTE
>  	 */
> -	if (!pte_present(pte) || !pte_user(pte) || !pte_read(pte))
> +	if (!pte_present(pte) || !pte_read(pte))
>  		return false;
>  
>  	if (write && !pte_write(pte))
> diff --git a/arch/powerpc/mm/ioremap.c b/arch/powerpc/mm/ioremap.c
> index 7823c38f09de..7b0afcabd89f 100644
> --- a/arch/powerpc/mm/ioremap.c
> +++ b/arch/powerpc/mm/ioremap.c
> @@ -50,10 +50,6 @@ void __iomem *ioremap_prot(phys_addr_t addr, size_t size, unsigned long flags)
>  	if (pte_write(pte))
>  		pte = pte_mkdirty(pte);
>  
> -	/* we don't want to let _PAGE_USER leak out */
> -	if (WARN_ON(pte_user(pte)))
> -		return NULL;
>

This check is still valid right? I understand that we want to remove
_PAGE_USER. But then loosing this check is ok? 

> -
>  	if (iowa_is_active())
>  		return iowa_ioremap(addr, size, pte_pgprot(pte), caller);
>  	return __ioremap_caller(addr, size, pte_pgprot(pte), caller);
> -- 
> 2.41.0