Subject: [PATCH] ARM: decompressor: ensure I-side picks up relocated code

From: [email-masked] (Florian Fainelli)
Date: Thu, 30 Oct 2014 12:28:14 -0700

On 10/30/2014 09:54 AM, Will Deacon wrote:
> To speed up decompression, the decompressor sets up a flat, cacheable
> mapping of memory. However, when there is insufficient space to hold
> the page tables for this mapping, we don't bother to enable the caches
> and subsequently skip all the cache maintenance hooks.
> 
> Skipping the cache maintenance before jumping to the relocated code
> allows the processor to predict the branch and populate the I-cache
> with stale data before the relocation loop has completed (since a
> bootloader may have SCTLR.I set, which permits normal, cacheable
> instruction fetches regardless of SCTLR.M).
> 
> This patch moves the cache maintenance check into the maintenance
> routines themselves, allowing the v6/v7 versions to invalidate the
> I-cache regardless of the MMU state.
> 
> Cc: Julien Grall <[email-masked]>
> Signed-off-by: Will Deacon <[email-masked]>

I guess we could credit Marc as well for reporting and providing early
patches addressing this?

http://comments.gmane.org/gmane.linux.ports.arm.kernel/347950

> ---
> 
> This fixes boot on my TC2 w/ multi_v7_defconfig. Julien was also
> reporting decompressor failures with a Xen payload, so hopefully this
> helps him too. If so, this is probably a candidate for stable.
> 
>  arch/arm/boot/compressed/head.S | 20 ++++++++++++++++----
>  1 file changed, 16 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
> index 413fd94b5301..68be9017593d 100644
> --- a/arch/arm/boot/compressed/head.S
> +++ b/arch/arm/boot/compressed/head.S
> @@ -397,8 +397,7 @@ dtb_check_done:
>  		add	sp, sp, r6
>  #endif
>  
> -		tst	r4, #1
> -		bleq	cache_clean_flush
> +		bl	cache_clean_flush
>  
>  		adr	r0, BSYM(restart)
>  		add	r0, r0, r6
> @@ -1047,6 +1046,8 @@ cache_clean_flush:
>  		b	call_cache_fn
>  
>  __armv4_mpu_cache_flush:
> +		tst	r4, #1
> +		movne	pc, lr
>  		mov	r2, #1
>  		mov	r3, #0
>  		mcr	p15, 0, ip, c7, c6, 0	@ invalidate D cache
> @@ -1064,6 +1065,8 @@ __armv4_mpu_cache_flush:
>  		mov	pc, lr
>  		
>  __fa526_cache_flush:
> +		tst	r4, #1
> +		movne	pc, lr
>  		mov	r1, #0
>  		mcr	p15, 0, r1, c7, c14, 0	@ clean and invalidate D cache
>  		mcr	p15, 0, r1, c7, c5, 0	@ flush I cache
> @@ -1072,13 +1075,16 @@ __fa526_cache_flush:
>  
>  __armv6_mmu_cache_flush:
>  		mov	r1, #0
> -		mcr	p15, 0, r1, c7, c14, 0	@ clean+invalidate D
> +		tst	r4, #1
> +		mcreq	p15, 0, r1, c7, c14, 0	@ clean+invalidate D
>  		mcr	p15, 0, r1, c7, c5, 0	@ invalidate I+BTB
> -		mcr	p15, 0, r1, c7, c15, 0	@ clean+invalidate unified
> +		mcreq	p15, 0, r1, c7, c15, 0	@ clean+invalidate unified
>  		mcr	p15, 0, r1, c7, c10, 4	@ drain WB
>  		mov	pc, lr
>  
>  __armv7_mmu_cache_flush:
> +		tst	r4, #1
> +		bne	iflush
>  		mrc	p15, 0, r10, c0, c1, 5	@ read ID_MMFR1
>  		tst	r10, #0xf << 16		@ hierarchical cache (ARMv7)
>  		mov	r10, #0
> @@ -1139,6 +1145,8 @@ iflush:
>  		mov	pc, lr
>  
>  __armv5tej_mmu_cache_flush:
> +		tst	r4, #1
> +		movne	pc, lr
>  1:		mrc	p15, 0, r15, c7, c14, 3	@ test,clean,invalidate D cache
>  		bne	1b
>  		mcr	p15, 0, r0, c7, c5, 0	@ flush I cache
> @@ -1146,6 +1154,8 @@ __armv5tej_mmu_cache_flush:
>  		mov	pc, lr
>  
>  __armv4_mmu_cache_flush:
> +		tst	r4, #1
> +		movne	pc, lr
>  		mov	r2, #64*1024		@ default: 32K dcache size (*2)
>  		mov	r11, #32		@ default: 32 byte line size
>  		mrc	p15, 0, r3, c0, c0, 1	@ read cache type
> @@ -1179,6 +1189,8 @@ no_cache_id:
>  
>  __armv3_mmu_cache_flush:
>  __armv3_mpu_cache_flush:
> +		tst	r4, #1
> +		movne	pc, lr
>  		mov	r1, #0
>  		mcr	p15, 0, r1, c7, c0, 0	@ invalidate whole cache v3
>  		mov	pc, lr
>