From: Catalin Marinas <catalin.marinas@arm.com>
To: Steve Capper <steve.capper@arm.com>
Cc: crecklin@redhat.com, ard.biesheuvel@linaro.org,
marc.zyngier@arm.com, bhsharma@redhat.com, will.deacon@arm.com,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 12/12] arm64: mm: Introduce 52-bit Kernel VAs
Date: Wed, 5 Jun 2019 16:34:41 +0100 [thread overview]
Message-ID: <20190605153441.GC50849@arrakis.emea.arm.com> (raw)
In-Reply-To: <20190528161026.13193-13-steve.capper@arm.com>
Hi Steve,
On Tue, May 28, 2019 at 05:10:26PM +0100, Steve Capper wrote:
> config ARM64_USER_VA_BITS_52
> bool "52-bit (user)"
> depends on ARM64_64K_PAGES && (ARM64_PAN || !ARM64_SW_TTBR0_PAN)
> + select HAS_VA_BITS_52
> help
> Enable 52-bit virtual addressing for userspace when explicitly
> requested via a hint to mmap(). The kernel will continue to
> @@ -751,11 +755,28 @@ config ARM64_USER_VA_BITS_52
>
> If unsure, select 48-bit virtual addressing instead.
>
> +config ARM64_USER_KERNEL_VA_BITS_52
> + bool "52-bit (user & kernel)"
> + depends on ARM64_64K_PAGES && (ARM64_PAN || !ARM64_SW_TTBR0_PAN)
> + select HAS_VA_BITS_52
> + help
> + Enable 52-bit virtual addressing for userspace when explicitly
> + requested via a hint to mmap(). The kernel will also use 52-bit
> + virtual addresses for its own mappings (provided HW support for
> + this feature is available, otherwise it reverts to 48-bit).
> +
> + NOTE: Enabling 52-bit virtual addressing in conjunction with
> + ARMv8.3 Pointer Authentication will result in the PAC being
> + reduced from 7 bits to 3 bits, which may have a significant
> + impact on its susceptibility to brute-force attacks.
> +
> + If unsure, select 48-bit virtual addressing instead.
With the latest version of this series, it doesn't look like will get a
performance hit for enabling 52-bit VA for the kernel (well, subject to
some testing). If that's the case, is it still worth having separate
user and user+kernel 52-bit VA Kconfig entries? It also gets pretty
confusing as I think you can now select both or just the latter for the
same feature.
BTW, do you plan to repost following comments? At a quick look, the
reset of the patches seem fine to me.
Thanks.
--
Catalin
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next prev parent reply other threads:[~2019-06-05 15:34 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-28 16:10 [PATCH v2 00/12] 52-bit kernel + user VAs Steve Capper
2019-05-28 16:10 ` [PATCH v2 01/12] arm/arm64: KVM: Formalise end of direct linear map Steve Capper
2019-05-28 16:27 ` Marc Zyngier
2019-05-28 17:01 ` Steve Capper
2019-05-29 9:26 ` Steve Capper
2019-05-28 16:10 ` [PATCH v2 02/12] arm64: mm: Flip kernel VA space Steve Capper
2019-05-28 16:10 ` [PATCH v2 03/12] arm64: kasan: Switch to using KASAN_SHADOW_OFFSET Steve Capper
2019-05-28 16:10 ` [PATCH v2 04/12] arm64: mm: Replace fixed map BUILD_BUG_ON's with BUG_ON's Steve Capper
2019-05-28 17:07 ` Ard Biesheuvel
2019-05-28 17:11 ` Ard Biesheuvel
2019-05-29 9:28 ` Steve Capper
2019-05-28 16:10 ` [PATCH v2 05/12] arm64: dump: Make kernel page table dumper dynamic again Steve Capper
2019-05-28 16:10 ` [PATCH v2 06/12] arm64: mm: Introduce VA_BITS_MIN Steve Capper
2019-05-28 16:10 ` [PATCH v2 07/12] arm64: mm: Introduce VA_BITS_ACTUAL Steve Capper
2019-05-28 16:10 ` [PATCH v2 08/12] arm64: mm: Logic to make offset_ttbr1 conditional Steve Capper
2019-06-10 14:18 ` Catalin Marinas
2019-06-12 10:58 ` Steve Capper
2019-05-28 16:10 ` [PATCH v2 09/12] arm64: mm: Separate out vmemmap Steve Capper
2019-05-28 16:10 ` [PATCH v2 10/12] arm64: mm: Modify calculation of VMEMMAP_SIZE Steve Capper
2019-05-28 16:10 ` [PATCH v2 11/12] arm64: mm: Tweak PAGE_OFFSET logic Steve Capper
2019-05-28 16:10 ` [PATCH v2 12/12] arm64: mm: Introduce 52-bit Kernel VAs Steve Capper
2019-06-05 15:34 ` Catalin Marinas [this message]
2019-06-07 10:34 ` Steve Capper
2019-06-07 13:53 ` [PATCH v2 00/12] 52-bit kernel + user VAs Anshuman Khandual
2019-06-07 14:24 ` Steve Capper
2019-06-10 10:40 ` Bhupesh Sharma
2019-06-10 10:40 ` Bhupesh Sharma
2019-06-10 10:54 ` Catalin Marinas
2019-06-10 10:54 ` Catalin Marinas
2019-06-10 11:15 ` Bhupesh Sharma
2019-06-10 11:15 ` Bhupesh Sharma
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