[PATCH 1/3] arm64: mm: Support Common Not Private translations

From: james.morse@arm.com (James Morse)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 1/3] arm64: mm: Support Common Not Private translations
Date: Tue, 10 Oct 2017 16:19:46 +0100	[thread overview]
Message-ID: <59DCE512.8010106@arm.com> (raw)
In-Reply-To: <1507553734-27854-2-git-send-email-vladimir.murzin@arm.com>

Hi Vladimir,

On 09/10/17 13:55, Vladimir Murzin wrote:
> Common Not Private (CNP) is a feature of ARMv8.2 extension which
> allows translation table entries to be shared between different PEs in
> the same inner shareable domain, so the hardware can use this fact to
> optimise the caching of such entries in the TLB.

> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 21e2c95..8d098a1 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -1211,6 +1224,14 @@ cpufeature_pan_not_uao(const struct arm64_cpu_capabilities *entry, int __unused)
>  	return (cpus_have_const_cap(ARM64_HAS_PAN) && !cpus_have_const_cap(ARM64_HAS_UAO));
>  }
>  
> +#ifdef CONFIG_ARM64_CNP
> +static int cpu_enable_cnp(void *__unused)
> +{
> +	cpu_replace_ttbr1(swapper_pg_dir);

All the other callers of cpu_replace_ttbr1() wrap swapper_pg_dir in lm_alias().
I'm pretty sure this is so that virt_to_phys() works when swapper_pg_dir's
address is in the vmalloc range.

CONFIG_DEBUG_VIRTUAL should catch problems like this.

(Nit: you shouldn't need the #ifdeffery, the only caller of this function is in
the same file, so the compiler should do the right thing)

> +	return 0;
> +}
> +#endif /* CONFIG_ARM64_CNP */
> +
>  /*
>   * We emulate only the following system register space.
>   * Op0 = 0x3, CRn = 0x0, Op1 = 0x0, CRm = [0, 4 - 7]