linux-kernel - Re: [PATCH 01/11] Initialize the mapping of KASan shadow memory

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Message-ID: <757534e5-fcea-3eb4-3c8d-b8c7e709f555@arm.com>
Date:   Wed, 22 Nov 2017 13:06:18 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     "Liuwenliang (Abbott Liu)" <liuwenliang@...wei.com>,
        Mark Rutland <mark.rutland@....com>
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Subject: Re: [PATCH 01/11] Initialize the mapping of KASan shadow memory

On 22/11/17 12:56, Liuwenliang (Abbott Liu) wrote:
> On Nov 22, 2017  20:30  Mark Rutland [mailto:mark.rutland@....com] wrote:
>> On Tue, Nov 21, 2017 at 07:59:01AM +0000, Liuwenliang (Abbott Liu) wrote:
>>> On Nov 17, 2017  21:49  Marc Zyngier [mailto:marc.zyngier@....com]  wrote:
>>>> On Sat, 18 Nov 2017 10:40:08 +0000
>>>> "Liuwenliang (Abbott Liu)" <liuwenliang@...wei.com> wrote:
>>>>> On Nov 17, 2017  15:36 Christoffer Dall [mailto:cdall@...aro.org]  wrote:
> 
>>> Please don't ask people to limit to 4GB of physical space on CPU
>>> supporting LPAE, please don't ask people to guaranteed to have some
>>> memory below 4GB on CPU supporting LPAE.
> 
>> I don't think that Marc is suggesting that you'd always use the 32-bit
>> accessors on an LPAE system, just that all the definitions should exist
>> regardless of configuration.
> 
>> So rather than this:
> 
>>> +#ifdef CONFIG_ARM_LPAE
>>> +#define TTBR0           __ACCESS_CP15_64(0, c2)
>>> +#define TTBR1           __ACCESS_CP15_64(1, c2)
>>> +#define PAR             __ACCESS_CP15_64(0, c7)
>>> +#else
>>> +#define TTBR0           __ACCESS_CP15(c2, 0, c0, 0)
>>> +#define TTBR1           __ACCESS_CP15(c2, 0, c0, 1)
>>> +#define PAR             __ACCESS_CP15(c7, 0, c4, 0)
>>> +#endif
> 
>> ... you'd have the following in cp15.h:
> 
>> #define TTBR0_64       __ACCESS_CP15_64(0, c2)
>> #define TTBR1_64       __ACCESS_CP15_64(1, c2)
>> #define PAR_64         __ACCESS_CP15_64(0, c7)
> 
>> #define TTBR0_32       __ACCESS_CP15(c2, 0, c0, 0)
>> #define TTBR1_32       __ACCESS_CP15(c2, 0, c0, 1)
>> #define PAR_32         __ACCESS_CP15(c7, 0, c4, 0)
> 
>> ... and elsewhere, where it matters, we choose which to use depending on
>> the kernel configuration, e.g.
> 
>> void set_ttbr0(u64 val)
>> {
>>       if (IS_ENABLED(CONFIG_ARM_LPAE))
>>               write_sysreg(val, TTBR0_64);
>>       else
>>               write_sysreg(val, TTBR0_32);
>> }
> 
>> Thanks,
>> Mark.
> 
> Thanks for your solution.
> I didn't know there was a IS_ENABLED macro that I can use, so I can't write a function 
> like:
> void set_ttbr0(u64 val)
> {
>        if (IS_ENABLED(CONFIG_ARM_LPAE))
>                write_sysreg(val, TTBR0_64);
>        else
>                write_sysreg(val, TTBR0_32);
> }
> 
> 
> Here is the code I tested on vexpress_a9 and vexpress_a15:
> diff --git a/arch/arm/include/asm/cp15.h b/arch/arm/include/asm/cp15.h
> index dbdbce1..5eb0185 100644
> --- a/arch/arm/include/asm/cp15.h
> +++ b/arch/arm/include/asm/cp15.h
> @@ -2,6 +2,7 @@
>  #define __ASM_ARM_CP15_H
> 
>  #include <asm/barrier.h>
> +#include <linux/stringify.h>
> 
>  /*
>   * CR1 bits (CP#15 CR1)
> @@ -64,8 +65,93 @@
>  #define __write_sysreg(v, r, w, c, t)  asm volatile(w " " c : : "r" ((t)(v)))
>  #define write_sysreg(v, ...)           __write_sysreg(v, __VA_ARGS__)
> 
> +#define TTBR0_32           __ACCESS_CP15(c2, 0, c0, 0)
> +#define TTBR1_32           __ACCESS_CP15(c2, 0, c0, 1)
> +#define TTBR0_64           __ACCESS_CP15_64(0, c2)
> +#define TTBR1_64           __ACCESS_CP15_64(1, c2)
> +#define PAR             __ACCESS_CP15_64(0, c7)

Please define both PAR accessors. Yes, I know the 32bit version is not
used yet, but it doesn't hurt to make it visible.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...