linux-kernel - Re: [PATCH] arm64: mm: Remove MAX_USER_VA

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Date:   Wed, 6 Nov 2019 11:23:11 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Bhupesh Sharma <bhsharma@...hat.com>
Cc:     linux-arm-kernel@...ts.infradead.org, bhupesh.linux@...il.com,
        James Morse <james.morse@....com>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will@...nel.org>,
        Steve Capper <steve.capper@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-kernel@...r.kernel.org, kexec@...ts.infradead.org
Subject: Re: [PATCH] arm64: mm: Remove MAX_USER_VA_BITS definition

On Tue, Nov 05, 2019 at 03:26:46AM +0530, Bhupesh Sharma wrote:
> commit 9b31cf493ffa ("arm64: mm: Introduce MAX_USER_VA_BITS definition")
> introduced the MAX_USER_VA_BITS definition, which was used to support
> the arm64 mm use-cases where the user-space could use 52-bit virtual
> addresses whereas the kernel-space would still could a maximum of 48-bit
> virtual addressing.
> 
> But, now with commit b6d00d47e81a ("arm64: mm: Introduce 52-bit Kernel
> VAs"), we removed the 52-bit user/48-bit kernel kconfig option and hence
> there is no longer any scenario where user VA != kernel VA size
> (even with CONFIG_ARM64_FORCE_52BIT enabled, the same is true).
> 
> Hence we can do away with the MAX_USER_VA_BITS macro as it is equal to
> VA_BITS (maximum VA space size) in all possible use-cases. Note that
> even though the 'vabits_actual' value would be 48 for arm64 hardware
> which don't support LVA-8.2 extension (even when CONFIG_ARM64_VA_BITS_52
> is enabled), VA_BITS would still be set to a value 52. Hence this change
> would be safe in all possible VA address space combinations.
> 
> Cc: James Morse <james.morse@....com>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Steve Capper <steve.capper@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> Cc: linux-kernel@...r.kernel.org
> Cc: kexec@...ts.infradead.org
> Signed-off-by: Bhupesh Sharma <bhsharma@...hat.com>

Queued for 5.5. Thanks.

-- 
Catalin