On Mon, Feb 01, 2016 at 05:28:32PM +0000, Marc Zyngier wrote:

On 01/02/16 17:08, Ard Biesheuvel wrote:

quoted

On 1 February 2016 at 17:20, Marc Zyngier [off-list ref] wrote:

quoted

On 01/02/16 15:36, Catalin Marinas wrote:

quoted

On Mon, Feb 01, 2016 at 01:34:16PM +0000, Marc Zyngier wrote:

quoted

On 01/02/16 13:16, Christoffer Dall wrote:

quoted

On Mon, Jan 25, 2016 at 03:53:40PM +0000, Marc Zyngier wrote:

quoted

diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
index 93e8d983..9e0683f 100644
--- a/arch/arm64/kvm/hyp/hyp-entry.S
+++ b/arch/arm64/kvm/hyp/hyp-entry.S

@@ -38,6 +38,32 @@
   ldp     x0, x1, [sp], #16
 .endm

+.macro do_el2_call
+  /*
+   * Shuffle the parameters before calling the function
+   * pointed to in x0. Assumes parameters in x[1,2,3].
+   */
+  stp     lr, xzr, [sp, #-16]!

remind me why this pair isn't just doing "str" instead of "stp" with the
xzr ?

Because SP has to be aligned on a 16 bytes boundary at all times.

You could do something like:

      sub     sp, sp, #16
      str     lr, [sp]

Ah, fair enough. I'll fold that in.

Since we're micro-reviewing: what's wrong with

str lr, [sp, #-16]!

?

I suspect that on most micro-architectures, a register writeback is
going to be slower than doing the sub independently.

I may be wrong, though.

For the record, I don't mind it the way it was in the original patch
either, I was just curious about the store of xzr and had forgottten the
stack alignment thing.

-Christoffer