Subject: [RFC PATCH] arm/arm64: KVM: Fix BE accesses to GICv2 EISR and ELRSR regs

From: [email-masked] (Andre Przywara)
Date: Wed, 01 Oct 2014 17:55:26 +0100

Hi Christoffer,

On 28/09/14 15:04, Christoffer Dall wrote:
> The EIRSR and ELRSR registers are 32-bit registers on GICv2, and we
> store these as an array of two such registers on the vgic vcpu struct.
> However, we access them as a single 64-bit value or as a bitmap pointer
> in the generic vgic code, which breaks BE support.
> 
> Instead, store them as u64 values on the vgic structure and do the
> word-swapping in the assembly code, which already handles the byte order
> for BE systems.

I am wondering if that approach isn't too involved.
EISR and ELRSR are 32-bit registers, and AFAIK the GIC is always LE on
the hardware side. So by claiming we have a 64bit register we introduce
too much hassle, right?
Wouldn't it be better to just fix the registers shortly before we
actually use them?
With my limited endianess experience: Wouldn't this patch solve the EISR
part (copy & pasted, so "for eyes only" ;-)

@@ -92,13 +89,10 @@ static u64 vgic_v2_get_eisr(const struct kvm_vcpu *vcpu)
 {
 	u64 val;

-#if BITS_PER_LONG == 64
-	val  = vcpu->arch.vgic_cpu.vgic_v2.vgic_eisr[1];
+       val  = le32_to_cpu(vcpu->arch.vgic_cpu.vgic_v2.vgic_eisr[1]);
        val <<= 32;
-       val |= vcpu->arch.vgic_cpu.vgic_v2.vgic_eisr[0];
-#else
-       val = *(u64 *)vcpu->arch.vgic_cpu.vgic_v2.vgic_eisr;
-#endif
+       val |= le32_to_cpu(vcpu->arch.vgic_cpu.vgic_v2.vgic_eisr[0]);
+
        return val;
 }

(BTW: Wasn't that 64 bit optimization path the wrong way round here?)

Please bear with me if this is complete nonsense, could well twisted my
mind once too much ;-)

Still thinking about a clever solution for that strange sync_elrsr()
thing ...

Cheers,
Andre.

> 
> Signed-off-by: Christoffer Dall <[email-masked]>
> ---
> I don't have a working BE configuration, so sending this out as an
> *UNTESTED on BE* RFC in hoping that someone with a working setup can
> give it a test for me (Will tells me Virtio is broken with kvmtool no BE
> hosts though), and to avoid someone else also doing this work.
> 
>  arch/arm/kvm/interrupts_head.S  |  7 +++++++
>  arch/arm64/kvm/vgic-v2-switch.S | 12 ++++++++----
>  include/kvm/arm_vgic.h          |  4 ++--
>  virt/kvm/arm/vgic-v2.c          | 24 +++---------------------
>  virt/kvm/arm/vgic.c             | 18 ++++++++++++++++--
>  5 files changed, 36 insertions(+), 29 deletions(-)
> 
> diff --git a/arch/arm/kvm/interrupts_head.S b/arch/arm/kvm/interrupts_head.S
> index 98c8c5b..14d4883 100644
> --- a/arch/arm/kvm/interrupts_head.S
> +++ b/arch/arm/kvm/interrupts_head.S
> @@ -433,10 +433,17 @@ ARM_BE8(rev	r10, r10	)
>  	str	r3, [r11, #VGIC_V2_CPU_HCR]
>  	str	r4, [r11, #VGIC_V2_CPU_VMCR]
>  	str	r5, [r11, #VGIC_V2_CPU_MISR]
> +#ifdef CONFIG_CPU_ENDIAN_BE8
> +	str	r6, [r11, #(VGIC_V2_CPU_EISR + 4)]
> +	str	r7, [r11, #VGIC_V2_CPU_EISR]
> +	str	r8, [r11, #(VGIC_V2_CPU_ELRSR + 4)]
> +	str	r9, [r11, #VGIC_V2_CPU_ELRSR]
> +#else
>  	str	r6, [r11, #VGIC_V2_CPU_EISR]
>  	str	r7, [r11, #(VGIC_V2_CPU_EISR + 4)]
>  	str	r8, [r11, #VGIC_V2_CPU_ELRSR]
>  	str	r9, [r11, #(VGIC_V2_CPU_ELRSR + 4)]
> +#endif
>  	str	r10, [r11, #VGIC_V2_CPU_APR]
>  
>  	/* Clear GICH_HCR */
> diff --git a/arch/arm64/kvm/vgic-v2-switch.S b/arch/arm64/kvm/vgic-v2-switch.S
> index ae21177..f002fe1 100644
> --- a/arch/arm64/kvm/vgic-v2-switch.S
> +++ b/arch/arm64/kvm/vgic-v2-switch.S
> @@ -67,10 +67,14 @@ CPU_BE(	rev	w11, w11 )
>  	str	w4, [x3, #VGIC_V2_CPU_HCR]
>  	str	w5, [x3, #VGIC_V2_CPU_VMCR]
>  	str	w6, [x3, #VGIC_V2_CPU_MISR]
> -	str	w7, [x3, #VGIC_V2_CPU_EISR]
> -	str	w8, [x3, #(VGIC_V2_CPU_EISR + 4)]
> -	str	w9, [x3, #VGIC_V2_CPU_ELRSR]
> -	str	w10, [x3, #(VGIC_V2_CPU_ELRSR + 4)]
> +CPU_LE(	str	w7, [x3, #VGIC_V2_CPU_EISR] )
> +CPU_LE(	str	w8, [x3, #(VGIC_V2_CPU_EISR + 4)] )
> +CPU_LE(	str	w9, [x3, #VGIC_V2_CPU_ELRSR] )
> +CPU_LE(	str	w10, [x3, #(VGIC_V2_CPU_ELRSR + 4)] )
> +CPU_BE(	str	w7, [x3, #(VGIC_V2_CPU_EISR + 4)] )
> +CPU_BE(	str	w8, [x3, #VGIC_V2_CPU_EISR] )
> +CPU_BE(	str	w9, [x3, #(VGIC_V2_CPU_ELRSR + 4)] )
> +CPU_BE(	str	w10, [x3, #VGIC_V2_CPU_ELRSR] )
>  	str	w11, [x3, #VGIC_V2_CPU_APR]
>  
>  	/* Clear GICH_HCR */
> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
> index 35b0c12..c66dc9ed 100644
> --- a/include/kvm/arm_vgic.h
> +++ b/include/kvm/arm_vgic.h
> @@ -168,8 +168,8 @@ struct vgic_v2_cpu_if {
>  	u32		vgic_hcr;
>  	u32		vgic_vmcr;
>  	u32		vgic_misr;	/* Saved only */
> -	u32		vgic_eisr[2];	/* Saved only */
> -	u32		vgic_elrsr[2];	/* Saved only */
> +	u64		vgic_eisr;	/* Saved only */
> +	u64		vgic_elrsr;	/* Saved only */
>  	u32		vgic_apr;
>  	u32		vgic_lr[VGIC_V2_MAX_LRS];
>  };
> diff --git a/virt/kvm/arm/vgic-v2.c b/virt/kvm/arm/vgic-v2.c
> index 416baed..2935405 100644
> --- a/virt/kvm/arm/vgic-v2.c
> +++ b/virt/kvm/arm/vgic-v2.c
> @@ -71,35 +71,17 @@ static void vgic_v2_sync_lr_elrsr(struct kvm_vcpu *vcpu, int lr,
>  				  struct vgic_lr lr_desc)
>  {
>  	if (!(lr_desc.state & LR_STATE_MASK))
> -		__set_bit(lr, (unsigned long *)vcpu->arch.vgic_cpu.vgic_v2.vgic_elrsr);
> +		vcpu->arch.vgic_cpu.vgic_v2.vgic_elrsr |= (1ULL << lr);
>  }
>  
>  static u64 vgic_v2_get_elrsr(const struct kvm_vcpu *vcpu)
>  {
> -	u64 val;
> -
> -#if BITS_PER_LONG == 64
> -	val  = vcpu->arch.vgic_cpu.vgic_v2.vgic_elrsr[1];
> -	val <<= 32;
> -	val |= vcpu->arch.vgic_cpu.vgic_v2.vgic_elrsr[0];
> -#else
> -	val = *(u64 *)vcpu->arch.vgic_cpu.vgic_v2.vgic_elrsr;
> -#endif
> -	return val;
> +	return vcpu->arch.vgic_cpu.vgic_v2.vgic_elrsr;
>  }
>  
>  static u64 vgic_v2_get_eisr(const struct kvm_vcpu *vcpu)
>  {
> -	u64 val;
> -
> -#if BITS_PER_LONG == 64
> -	val  = vcpu->arch.vgic_cpu.vgic_v2.vgic_eisr[1];
> -	val <<= 32;
> -	val |= vcpu->arch.vgic_cpu.vgic_v2.vgic_eisr[0];
> -#else
> -	val = *(u64 *)vcpu->arch.vgic_cpu.vgic_v2.vgic_eisr;
> -#endif
> -	return val;
> +	return vcpu->arch.vgic_cpu.vgic_v2.vgic_eisr;
>  }
>  
>  static u32 vgic_v2_get_interrupt_status(const struct kvm_vcpu *vcpu)
> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
> index 73eba79..30cf369 100644
> --- a/virt/kvm/arm/vgic.c
> +++ b/virt/kvm/arm/vgic.c
> @@ -118,6 +118,20 @@ static const struct vgic_params *vgic;
>  #define REG_OFFSET_SWIZZLE	0
>  #endif
>  
> +/*
> + * Call this function to convert a u64 value to an unsigned long * bitmask
> + * in a way that works on both 32-bit and 64-bit LE and BE platforms.
> + *
> + * Warning: Calling this function may modify *val.
> + */
> +static unsigned long *u64_to_bitmask(u64 *val)
> +{
> +#if defined(CONFIG_CPU_BIG_ENDIAN) && BITS_PER_LONG == 32
> +	*val = (*val >> 32) | (*val << 32);
> +#endif
> +	return (unsigned long *)val;
> +}
> +
>  static u32 *vgic_bitmap_get_reg(struct vgic_bitmap *x,
>  				int cpuid, u32 offset)
>  {
> @@ -1256,7 +1270,7 @@ static bool vgic_process_maintenance(struct kvm_vcpu *vcpu)
>  		 * active bit.
>  		 */
>  		u64 eisr = vgic_get_eisr(vcpu);
> -		unsigned long *eisr_ptr = (unsigned long *)&eisr;
> +		unsigned long *eisr_ptr = u64_to_bitmask(&eisr);
>  		int lr;
>  
>  		for_each_set_bit(lr, eisr_ptr, vgic->nr_lr) {
> @@ -1304,7 +1318,7 @@ static void __kvm_vgic_sync_hwstate(struct kvm_vcpu *vcpu)
>  
>  	level_pending = vgic_process_maintenance(vcpu);
>  	elrsr = vgic_get_elrsr(vcpu);
> -	elrsr_ptr = (unsigned long *)&elrsr;
> +	elrsr_ptr = u64_to_bitmask(&elrsr);
>  
>  	/* Clear mappings for empty LRs */
>  	for_each_set_bit(lr, elrsr_ptr, vgic->nr_lr) {
>