From: "Justin He (Arm Technology China)" <Justin.He@arm.com>
To: Catalin Marinas <Catalin.Marinas@arm.com>
Cc: "linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"x86@kernel.org" <x86@kernel.org>,
"hejianet@gmail.com" <hejianet@gmail.com>,
"Kaly Xin (Arm Technology China)" <Kaly.Xin@arm.com>,
nd <nd@arm.com>
Subject: RE: [PATCH v11 1/4] arm64: cpufeature: introduce helper cpu_has_hw_af()
Date: Fri, 11 Oct 2019 13:51:01 +0000 [thread overview]
Message-ID: <DB7PR08MB3082DDB5E28648F873D23493F7970@DB7PR08MB3082.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <20191011103857.GB54842@arrakis.emea.arm.com>
Hi Catanlin
Thanks for the detailed explanation.
Will send out v12 soon after testing
--
Cheers,
Justin (Jia He)
> -----Original Message-----
> From: Catalin Marinas <catalin.marinas@arm.com>
> Sent: Friday, October 11, 2019 6:39 PM
> To: Justin He (Arm Technology China) <Justin.He@arm.com>
> Cc: Will Deacon <will@kernel.org>; Mark Rutland
> <Mark.Rutland@arm.com>; James Morse <James.Morse@arm.com>; Marc
> Zyngier <maz@kernel.org>; Matthew Wilcox <willy@infradead.org>; Kirill A.
> Shutemov <kirill.shutemov@linux.intel.com>; linux-arm-
> kernel@lists.infradead.org; linux-kernel@vger.kernel.org; linux-
> mm@kvack.org; Suzuki Poulose <Suzuki.Poulose@arm.com>; Borislav
> Petkov <bp@alien8.de>; H. Peter Anvin <hpa@zytor.com>; x86@kernel.org;
> Thomas Gleixner <tglx@linutronix.de>; Andrew Morton <akpm@linux-
> foundation.org>; hejianet@gmail.com; Kaly Xin (Arm Technology China)
> <Kaly.Xin@arm.com>; nd <nd@arm.com>
> Subject: Re: [PATCH v11 1/4] arm64: cpufeature: introduce helper
> cpu_has_hw_af()
>
> On Fri, Oct 11, 2019 at 01:16:36AM +0000, Justin He (Arm Technology China)
> wrote:
> > From: Catalin Marinas <catalin.marinas@arm.com>
> > > On Wed, Oct 09, 2019 at 04:42:43PM +0800, Jia He wrote:
> > > > + u64 mmfr1 = read_cpuid(ID_AA64MMFR1_EL1);
> > > > +
> > > > + return !!cpuid_feature_extract_unsigned_field(mmfr1,
> > > > +
> > > ID_AA64MMFR1_HADBS_SHIFT);
> > >
> > > No need for !!, the return type is a bool already.
> >
> > But cpuid_feature_extract_unsigned_field has the return type "unsigned
> int" [1]
> >
> > [1]
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch
> /arm64/include/asm/cpufeature.h#n444
>
> And the C language gives you the automatic conversion from unsigned int
> to bool without the need for !!. The reason we use !! in some places is
> for converting long to int (not bool) and losing the top 32-bit. See
> commit 84fe6826c28f ("arm64: mm: Add double logical invert to pte
> accessors") for an explanation.
>
> --
> Catalin
next prev parent reply other threads:[~2019-10-11 13:51 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-09 8:42 [PATCH v11 0/4] fix double page fault in cow_user_page for pfn mapping Jia He
2019-10-09 8:42 ` [PATCH v11 1/4] arm64: cpufeature: introduce helper cpu_has_hw_af() Jia He
2019-10-10 16:43 ` Catalin Marinas
2019-10-11 1:16 ` Justin He (Arm Technology China)
2019-10-11 10:38 ` Catalin Marinas
2019-10-11 13:51 ` Justin He (Arm Technology China) [this message]
2019-10-09 8:42 ` [PATCH v11 2/4] arm64: mm: implement arch_faults_on_old_pte() on arm64 Jia He
2019-10-09 8:42 ` [PATCH v11 3/4] x86/mm: implement arch_faults_on_old_pte() stub on x86 Jia He
2019-10-09 8:42 ` [PATCH v11 4/4] mm: fix double page fault on arm64 if PTE_AF is cleared Jia He
2019-10-10 16:45 ` Catalin Marinas
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