From: Steve Capper <Steve.Capper@arm.com>
To: Catalin Marinas <Catalin.Marinas@arm.com>
Cc: "crecklin@redhat.com" <crecklin@redhat.com>,
"ard.biesheuvel@linaro.org" <ard.biesheuvel@linaro.org>,
Marc Zyngier <Marc.Zyngier@arm.com>,
"bhsharma@redhat.com" <bhsharma@redhat.com>,
Will Deacon <Will.Deacon@arm.com>, nd <nd@arm.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v2 12/12] arm64: mm: Introduce 52-bit Kernel VAs
Date: Fri, 7 Jun 2019 10:34:15 +0000 [thread overview]
Message-ID: <20190607103353.GA1509@capper-debian.cambridge.arm.com> (raw)
In-Reply-To: <20190605153441.GC50849@arrakis.emea.arm.com>
On Wed, Jun 05, 2019 at 04:34:41PM +0100, Catalin Marinas wrote:
> Hi Steve,
Hi Catalin,
>
> 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.
Yeah, I was wondering if it would be better to just have a single
52-bit VA configuration entry. I think the performance should be fine.
>
> BTW, do you plan to repost following comments? At a quick look, the
> reset of the patches seem fine to me.
>
Thanks :-)
I'll repost another version of the series with a few simplifications
that Ard and Marc mentioned along with single 52-bit VA configuration
option.
Cheers,
--
Steve
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next prev parent reply other threads:[~2019-06-07 10:34 UTC|newest]
Thread overview: 28+ 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
2019-06-07 10:34 ` Steve Capper [this message]
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 10:54 ` Catalin Marinas
2019-06-10 11:15 ` Bhupesh Sharma
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