linux-kernel - Re: [PATCH] arm64: use mov_q instead of literal ldr

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Message-ID: <20200312164229.GB21120@lakrids.cambridge.arm.com>
Date:   Thu, 12 Mar 2020 16:42:30 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Rémi Denis-Courmont <remi@...lab.net>
Cc:     linux-arm-kernel@...ts.infradead.org, suzuki.poulose@....com,
        maz@...nel.org, linux-kernel@...r.kernel.org, james.morse@....com,
        catalin.marinas@....com, will@...nel.org,
        kvmarm@...ts.cs.columbia.edu, julien.thierry.kdev@...il.com
Subject: Re: [PATCH] arm64: use mov_q instead of literal ldr

On Thu, Mar 12, 2020 at 11:40:14AM +0200, Rémi Denis-Courmont wrote:
> From: Remi Denis-Courmont <remi.denis.courmont@...wei.com>
> 
> In practice, this requires only 2 instructions, or even only 1 for
> the idmap_pg_dir size (with 4 or 64 KiB pages). Only the MAIR values
> needed more than 2 instructions and it was already converted to mov_q
> by 95b3f74bec203804658e17f86fe20755bb8abcb9.
> 
> Signed-off-by: Remi Denis-Courmont <remi.denis.courmont@...wei.com>

FWIW:

Acked-by: Mark Rutland <mark.rutland@....com>

Mark.

> ---
>  arch/arm64/kernel/cpu-reset.S       |  2 +-
>  arch/arm64/kernel/hyp-stub.S        |  2 +-
>  arch/arm64/kernel/relocate_kernel.S |  4 +---
>  arch/arm64/kvm/hyp-init.S           | 10 ++++------
>  arch/arm64/mm/proc.S                |  2 +-
>  5 files changed, 8 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/arm64/kernel/cpu-reset.S b/arch/arm64/kernel/cpu-reset.S
> index 32c7bf858dd9..38087b4c0432 100644
> --- a/arch/arm64/kernel/cpu-reset.S
> +++ b/arch/arm64/kernel/cpu-reset.S
> @@ -32,7 +32,7 @@
>  ENTRY(__cpu_soft_restart)
>  	/* Clear sctlr_el1 flags. */
>  	mrs	x12, sctlr_el1
> -	ldr	x13, =SCTLR_ELx_FLAGS
> +	mov_q	x13, SCTLR_ELx_FLAGS
>  	bic	x12, x12, x13
>  	pre_disable_mmu_workaround
>  	msr	sctlr_el1, x12
> diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S
> index 73d46070b315..e473ead806ed 100644
> --- a/arch/arm64/kernel/hyp-stub.S
> +++ b/arch/arm64/kernel/hyp-stub.S
> @@ -63,7 +63,7 @@ el1_sync:
>  	beq	9f				// Nothing to reset!
>  
>  	/* Someone called kvm_call_hyp() against the hyp-stub... */
> -	ldr	x0, =HVC_STUB_ERR
> +	mov_q	x0, HVC_STUB_ERR
>  	eret
>  
>  9:	mov	x0, xzr
> diff --git a/arch/arm64/kernel/relocate_kernel.S b/arch/arm64/kernel/relocate_kernel.S
> index c1d7db71a726..c40ce496c78b 100644
> --- a/arch/arm64/kernel/relocate_kernel.S
> +++ b/arch/arm64/kernel/relocate_kernel.S
> @@ -41,7 +41,7 @@ ENTRY(arm64_relocate_new_kernel)
>  	cmp	x0, #CurrentEL_EL2
>  	b.ne	1f
>  	mrs	x0, sctlr_el2
> -	ldr	x1, =SCTLR_ELx_FLAGS
> +	mov_q	x1, SCTLR_ELx_FLAGS
>  	bic	x0, x0, x1
>  	pre_disable_mmu_workaround
>  	msr	sctlr_el2, x0
> @@ -113,8 +113,6 @@ ENTRY(arm64_relocate_new_kernel)
>  
>  ENDPROC(arm64_relocate_new_kernel)
>  
> -.ltorg
> -
>  .align 3	/* To keep the 64-bit values below naturally aligned. */
>  
>  .Lcopy_end:
> diff --git a/arch/arm64/kvm/hyp-init.S b/arch/arm64/kvm/hyp-init.S
> index 84f32cf5abc7..6e6ed5581eed 100644
> --- a/arch/arm64/kvm/hyp-init.S
> +++ b/arch/arm64/kvm/hyp-init.S
> @@ -60,7 +60,7 @@ alternative_else_nop_endif
>  	msr	ttbr0_el2, x4
>  
>  	mrs	x4, tcr_el1
> -	ldr	x5, =TCR_EL2_MASK
> +	mov_q	x5, TCR_EL2_MASK
>  	and	x4, x4, x5
>  	mov	x5, #TCR_EL2_RES1
>  	orr	x4, x4, x5
> @@ -102,7 +102,7 @@ alternative_else_nop_endif
>  	 * as well as the EE bit on BE. Drop the A flag since the compiler
>  	 * is allowed to generate unaligned accesses.
>  	 */
> -	ldr	x4, =(SCTLR_EL2_RES1 | (SCTLR_ELx_FLAGS & ~SCTLR_ELx_A))
> +	mov_q	x4, (SCTLR_EL2_RES1 | (SCTLR_ELx_FLAGS & ~SCTLR_ELx_A))
>  CPU_BE(	orr	x4, x4, #SCTLR_ELx_EE)
>  	msr	sctlr_el2, x4
>  	isb
> @@ -142,7 +142,7 @@ reset:
>  	 * case we coming via HVC_SOFT_RESTART.
>  	 */
>  	mrs	x5, sctlr_el2
> -	ldr	x6, =SCTLR_ELx_FLAGS
> +	mov_q	x6, SCTLR_ELx_FLAGS
>  	bic	x5, x5, x6		// Clear SCTL_M and etc
>  	pre_disable_mmu_workaround
>  	msr	sctlr_el2, x5
> @@ -155,11 +155,9 @@ reset:
>  	eret
>  
>  1:	/* Bad stub call */
> -	ldr	x0, =HVC_STUB_ERR
> +	mov_q	x0, HVC_STUB_ERR
>  	eret
>  
>  SYM_CODE_END(__kvm_handle_stub_hvc)
>  
> -	.ltorg
> -
>  	.popsection
> diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
> index 1b871f141eb4..6bd228067ebc 100644
> --- a/arch/arm64/mm/proc.S
> +++ b/arch/arm64/mm/proc.S
> @@ -411,7 +411,7 @@ SYM_FUNC_START(__cpu_setup)
>  	 * Set/prepare TCR and TTBR. We use 512GB (39-bit) address range for
>  	 * both user and kernel.
>  	 */
> -	ldr	x10, =TCR_TxSZ(VA_BITS) | TCR_CACHE_FLAGS | TCR_SMP_FLAGS | \
> +	mov_q	x10, TCR_TxSZ(VA_BITS) | TCR_CACHE_FLAGS | TCR_SMP_FLAGS | \
>  			TCR_TG_FLAGS | TCR_KASLR_FLAGS | TCR_ASID16 | \
>  			TCR_TBI0 | TCR_A1 | TCR_KASAN_FLAGS
>  	tcr_clear_errata_bits x10, x9, x5
> -- 
> 2.25.1
> 
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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