linux-kernel - Re: [PATCH 2/2] arm64/mm: Update create_kpti_ng_temp_pgd() to handle pgtable

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Message-ID: <34ce1000-8d15-4d7e-bf67-11e2bcd135a5@arm.com>
Date: Fri, 15 Aug 2025 14:00:06 +0200
From: Kevin Brodsky <kevin.brodsky@....com>
To: Chaitanya S Prakash <chaitanyas.prakash@....com>,
 linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Cc: Ryan Roberts <ryan.roberts@....com>,
 Yang Shi <yang@...amperecomputing.com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Anshuman Khandual <anshuman.khandual@....com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Zhenhua Huang <quic_zhenhuah@...cinc.com>, Joey Gouly <joey.gouly@....com>
Subject: Re: [PATCH 2/2] arm64/mm: Update create_kpti_ng_temp_pgd() to handle
 pgtable_alloc failure

On 13/08/2025 16:56, Chaitanya S Prakash wrote:
> create_kpti_ng_temp_pgd() was created as an alias for void returning
> __create_pgd_mapping_locked() and relied on pgtable_alloc() to BUG_ON()
> if an allocation failure occurred. But as __create_pgd_mapping_locked()
> has been updated as a part of the error propagation patch to return a
> non-void value, update create_kpti_ng_temp_pgd() to act as a wrapper
> around __create_pgd_mapping_locked() and BUG_ON() on ret being a non
> zero value.
>
> Signed-off-by: Chaitanya S Prakash <chaitanyas.prakash@....com>
> ---
>  arch/arm64/mm/mmu.c | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index db7f45ef16574..19cbabceb38bd 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -76,6 +76,14 @@ EXPORT_SYMBOL(empty_zero_page);
>  static DEFINE_SPINLOCK(swapper_pgdir_lock);
>  static DEFINE_MUTEX(fixmap_lock);
>  
> +#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
> +void create_kpti_ng_temp_pgd(pgd_t *pgdir, phys_addr_t phys,
> +			     unsigned long virt, phys_addr_t size,
> +			     pgprot_t prot,
> +			     phys_addr_t (*pgtable_alloc)(enum pgtable_type),
> +			     int flags);

I'm not sure I understand why we'd now need this declaration?

That function should really be declared in some header instead of the
strange declaration in cpufeature.c, but that's unrelated to this patch.

- Kevin

> +#endif
> +
>  void noinstr set_swapper_pgd(pgd_t *pgdp, pgd_t pgd)
>  {
>  	pgd_t *fixmap_pgdp;
> @@ -541,11 +549,17 @@ static void ___create_pgd_mapping(pgd_t *pgdir, phys_addr_t phys,
>  }
>  
>  #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
> -extern __alias(__create_pgd_mapping_locked)
>  void create_kpti_ng_temp_pgd(pgd_t *pgdir, phys_addr_t phys, unsigned long virt,
>  			     phys_addr_t size, pgprot_t prot,
>  			     phys_addr_t (*pgtable_alloc)(enum pgtable_type),
> -			     int flags);
> +			     int flags)
> +{
> +	int ret = 0;
> +
> +	ret = __create_pgd_mapping_locked(pgdir, phys, virt, size, prot,
> +					  pgtable_alloc, flags);
> +	BUG_ON(ret);
> +}
>  #endif
>  
>  static phys_addr_t __pgd_pgtable_alloc(struct mm_struct *mm,