linux-kernel - Re: [PATCH 15/16] arm64: Add a helper to retrieve the PTE of a fixmap

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Message-ID: <YPawgYJYfD+EfXBW@google.com>
Date:   Tue, 20 Jul 2021 12:16:17 +0100
From:   Quentin Perret <qperret@...gle.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org, will@...nel.org,
        dbrazdil@...gle.com, Srivatsa Vaddagiri <vatsa@...eaurora.org>,
        Shanker R Donthineni <sdonthineni@...dia.com>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        kernel-team@...roid.com
Subject: Re: [PATCH 15/16] arm64: Add a helper to retrieve the PTE of a fixmap

On Thursday 15 Jul 2021 at 17:31:58 (+0100), Marc Zyngier wrote:
> In order to transfer the early mapping state into KVM's MMIO
> guard infrastucture, provide a small helper that will retrieve
> the associated PTE.
> 
> Signed-off-by: Marc Zyngier <maz@...nel.org>
> ---
>  arch/arm64/include/asm/fixmap.h |  2 ++
>  arch/arm64/mm/mmu.c             | 15 +++++++++++++++
>  2 files changed, 17 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/fixmap.h b/arch/arm64/include/asm/fixmap.h
> index 4335800201c9..1aae625b944f 100644
> --- a/arch/arm64/include/asm/fixmap.h
> +++ b/arch/arm64/include/asm/fixmap.h
> @@ -105,6 +105,8 @@ void __init early_fixmap_init(void);
>  
>  extern void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot);
>  
> +extern pte_t *__get_fixmap_pte(enum fixed_addresses idx);
> +
>  #include <asm-generic/fixmap.h>
>  
>  #endif /* !__ASSEMBLY__ */
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index d74586508448..f1b7abd04025 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1286,6 +1286,21 @@ void __set_fixmap(enum fixed_addresses idx,
>  	}
>  }
>  
> +pte_t *__get_fixmap_pte(enum fixed_addresses idx)
> +{
> +	unsigned long 	addr = __fix_to_virt(idx);

Nit: odd spacing here.

> +	pte_t *ptep;
> +
> +	BUG_ON(idx <= FIX_HOLE || idx >= __end_of_fixed_addresses);
> +
> +	ptep = fixmap_pte(addr);
> +
> +	if (!pte_valid(*ptep))
> +		return NULL;
> +
> +	return ptep;
> +}
> +
>  void *__init fixmap_remap_fdt(phys_addr_t dt_phys, int *size, pgprot_t prot)
>  {
>  	const u64 dt_virt_base = __fix_to_virt(FIX_FDT);
> -- 
> 2.30.2
>