linux-kernel - Re: [PATCH V2] arm64: tlbflush: avoid writing RES0 bits

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Message-ID: <20180327173613.GI18435@arm.com>
Date:   Tue, 27 Mar 2018 18:36:13 +0100
From:   Will Deacon <will.deacon@....com>
To:     Shanker Donthineni <shankerd@...eaurora.org>
Cc:     Robin Murphy <robin.murphy@....com>,
        Philip Elcan <pelcan@...eaurora.org>,
        linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        linux-kernel@...r.kernel.org,
        Thomas Speier <tspeier@...eaurora.org>
Subject: Re: [PATCH V2] arm64: tlbflush: avoid writing RES0 bits

Hi Shanker,

On Tue, Mar 27, 2018 at 09:53:16AM -0500, Shanker Donthineni wrote:
> On 03/27/2018 06:34 AM, Robin Murphy wrote:
> > On 27/03/18 04:21, Philip Elcan wrote:
> >> Several of the bits of the TLBI register operand are RES0 per the ARM
> >> ARM, so TLBI operations should avoid writing non-zero values to these
> >> bits.
> >>
> >> This patch adds a macro __TLBI_VADDR(addr, asid) that creates the
> >> operand register in the correct format and honors the RES0 bits.
> >>
> >> Signed-off-by: Philip Elcan <pelcan@...eaurora.org>
> >> ---
> >>   arch/arm64/include/asm/tlbflush.h | 23 ++++++++++++++++-------
> >>   1 file changed, 16 insertions(+), 7 deletions(-)
> >>
> >> diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h
> >> index 9e82dd7..b1205e9 100644
> >> --- a/arch/arm64/include/asm/tlbflush.h
> >> +++ b/arch/arm64/include/asm/tlbflush.h
> >> @@ -60,6 +60,15 @@
> >>           __tlbi(op, (arg) | USER_ASID_FLAG);                \
> >>   } while (0)
> >>   +/* This macro creates a properly formatted VA operand for the TLBI */
> >> +#define __TLBI_VADDR(addr, asid)                \
> >> +    ({                            \
> >> +        unsigned long __ta = (addr) >> 12;        \
> >> +        __ta &= GENMASK_ULL(43, 0);            \
> >> +        __ta |= (unsigned long)(asid) << 48;        \
> >> +        __ta;                        \
> >> +    })
> > 
> > I'd be inclined to make this a static inline function rather than a
> > macro, since it doesn't need to do any wacky type-dodging, but either
> > way the overall change now looks appropriate;
> > 
> > Acked-by: Robin Murphy <robin.murphy@....com>
> > 
> 
> Tested-by: Shanker Donthineni <shankerd@...eaurora.org>

[...]

> >> @@ -154,8 +163,8 @@ static inline void __flush_tlb_range(struct vm_area_struct *vma,
> >>           return;
> >>       }
> >>   -    start = asid | (start >> 12);
> >> -    end = asid | (end >> 12);
> >> +    start = __TLBI_VADDR(start, asid);
> >> +    end = __TLBI_VADDR(end, asid);

Can you test this bit too, please? ;)

Will