[PATCH v4 04/19] arm/arm64: KVM: wrap 64 bit MMIO accesses with two 32 bit ones

[Christoffer Dall]

On Fri, Nov 14, 2014 at 10:07:48AM +0000, Andre Przywara wrote:
> Some GICv3 registers can and will be accessed as 64 bit registers.
> Currently the register handling code can only deal with 32 bit
> accesses, so we do two consecutive calls to cover this.
> 
> Signed-off-by: Andre Przywara <andre.przywara at arm.com>
> ---
> Changelog v3...v4:
> - add comment explaining little endian handling
> 
>  virt/kvm/arm/vgic.c |   51 ++++++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 48 insertions(+), 3 deletions(-)
> 
> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
> index 5eee3de..dba51e4 100644
> --- a/virt/kvm/arm/vgic.c
> +++ b/virt/kvm/arm/vgic.c
> @@ -1033,6 +1033,51 @@ static bool vgic_validate_access(const struct vgic_dist *dist,
>  }
>  
>  /*
> + * Call the respective handler function for the given range.
> + * We split up any 64 bit accesses into two consecutive 32 bit
> + * handler calls and merge the result afterwards.
> + * We do this in a little endian fashion regardless of the host's
> + * or guest's endianness, because the GIC is always LE and the rest of
> + * the code (vgic_reg_access) also puts it in a LE fashion already.
> + */
> +static bool call_range_handler(struct kvm_vcpu *vcpu,
> +			       struct kvm_exit_mmio *mmio,
> +			       unsigned long offset,
> +			       const struct mmio_range *range)
> +{
> +	u32 *data32 = (void *)mmio->data;
> +	struct kvm_exit_mmio mmio32;
> +	bool ret;
> +
> +	if (likely(mmio->len <= 4))
> +		return range->handle_mmio(vcpu, mmio, offset);
> +
> +	/*
> +	 * Any access bigger than 4 bytes (that we currently handle in KVM)
> +	 * is actually 8 bytes long, caused by a 64-bit access
> +	 */
> +
> +	mmio32.len = 4;
> +	mmio32.is_write = mmio->is_write;
> +
> +	mmio32.phys_addr = mmio->phys_addr + 4;
> +	if (mmio->is_write)
> +		*(u32 *)mmio32.data = data32[1];
> +	ret = range->handle_mmio(vcpu, &mmio32, offset + 4);
> +	if (!mmio->is_write)
> +		data32[1] = *(u32 *)mmio32.data;
> +
> +	mmio32.phys_addr = mmio->phys_addr;
> +	if (mmio->is_write)
> +		*(u32 *)mmio32.data = data32[0];
> +	ret |= range->handle_mmio(vcpu, &mmio32, offset);

nit: if handle_mmio returns multiple error codes, we will now not
(necessarily) be preserving either, so you may just want to do a check
on ret above and return early in the case of error.  Only worth it if
you respin anyway.

Otherwise:
Reviewed-by: Christoffer Dall <christoffer.dall at linaro.org>

> +	if (!mmio->is_write)
> +		data32[0] = *(u32 *)mmio32.data;
> +
> +	return ret;
> +}
> +
> +/*
>   * vgic_handle_mmio_range - handle an in-kernel MMIO access
>   * @vcpu:	pointer to the vcpu performing the access
>   * @run:	pointer to the kvm_run structure
> @@ -1063,10 +1108,10 @@ static bool vgic_handle_mmio_range(struct kvm_vcpu *vcpu, struct kvm_run *run,
>  	spin_lock(&vcpu->kvm->arch.vgic.lock);
>  	offset -= range->base;
>  	if (vgic_validate_access(dist, range, offset)) {
> -		updated_state = range->handle_mmio(vcpu, mmio, offset);
> +		updated_state = call_range_handler(vcpu, mmio, offset, range);
>  	} else {
> -		vgic_reg_access(mmio, NULL, offset,
> -				ACCESS_READ_RAZ | ACCESS_WRITE_IGNORED);
> +		if (!mmio->is_write)
> +			memset(mmio->data, 0, mmio->len);
>  		updated_state = false;
>  	}
>  	spin_unlock(&vcpu->kvm->arch.vgic.lock);
> -- 
> 1.7.9.5
>