[PATCH v4 11/14] ARM64: KVM: fix vgic_bitmap_get_reg function for BE 64bit case

On Sat, Jun 14 2014 at 04:04:51 PM, Christoffer Dall [off-list ref] wrote:

On Thu, Jun 12, 2014 at 09:30:10AM -0700, Victor Kamensky wrote:

quoted

Fix vgic_bitmap_get_reg function to return 'right' word address of
'unsigned long' bitmap value in case of BE 64bit image.

Signed-off-by: Victor Kamensky <redacted>
---
 virt/kvm/arm/vgic.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
index 529c336..b4ffd82 100644
--- a/virt/kvm/arm/vgic.c
+++ b/virt/kvm/arm/vgic.c

@@ -101,14 +101,34 @@ static u32 vgic_nr_lr;
 
 static unsigned int vgic_maint_irq;
 
+/*
+ * struct vgic_bitmap contains unions that provide two views of
+ * the same data. In one case it is an array of registers of
+ * u32's, and in the other case it is a bitmap of unsigned
+ * longs.
+ *
+ * This does not work on 64-bit BE systems, because the bitmap access
+ * will store two consecutive 32-bit words with the higher-addressed
+ * register's bits at the lower index and the lower-addressed register's
+ * bits at the higher index.
+ *
+ * Therefore, swizzle the register index when accessing the 32-bit word
+ * registers to access the right register's value.
+ */
+#if defined(CONFIG_CPU_BIG_ENDIAN) && BITS_PER_LONG == 64
+#define REG_OFFSET_SWIZZLE	1
+#else
+#define REG_OFFSET_SWIZZLE	0
+#endif
+
 static u32 *vgic_bitmap_get_reg(struct vgic_bitmap *x,
 				int cpuid, u32 offset)
 {
 	offset >>= 2;
 	if (!offset)
-		return x->percpu[cpuid].reg;
+		return x->percpu[cpuid].reg + (offset ^ REG_OFFSET_SWIZZLE);
 	else
-		return x->shared.reg + offset - 1;
+		return x->shared.reg + ((offset - 1) ^ REG_OFFSET_SWIZZLE);
 }
 
 static int vgic_bitmap_get_irq_val(struct vgic_bitmap *x,

-- 
1.8.1.4

I had wished there was a cleaner way to abstract this, but I can't think
of a cleaner solution, and restructuring the whole thing would be very
invasive.

I'm curious to hear from Marc on this one, but you can add:

Reviewed-by: Christoffer Dall <redacted>

because it looks correct.

Thanks for picking up my suggestion on the commenting.

I tried hard to find another solution, but I think this is unfortunately
the best we can have... ;-)

So:
        Acked-by: Marc Zyngier [off-list ref]

I will have to fold in a similar solution for the vgic-dyn series.

Thanks,

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