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

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

quoted

With VHE, the host never issues an HVC instruction to get into the
KVM code, as we can simply branch there.

Use runtime code patching to simplify things a bit.

Signed-off-by: Marc Zyngier <redacted>
---
 arch/arm64/kvm/hyp.S           |  7 +++++++
 arch/arm64/kvm/hyp/hyp-entry.S | 38 +++++++++++++++++++++++++++++---------
 2 files changed, 36 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S
index 0ccdcbb..0689a74 100644
--- a/arch/arm64/kvm/hyp.S
+++ b/arch/arm64/kvm/hyp.S

@@ -17,7 +17,9 @@
 
 #include <linux/linkage.h>
 
+#include <asm/alternative.h>
 #include <asm/assembler.h>
+#include <asm/cpufeature.h>
 
 /*
  * u64 kvm_call_hyp(void *hypfn, ...);

@@ -38,6 +40,11 @@
  * arch/arm64/kernel/hyp_stub.S.
  */
 ENTRY(kvm_call_hyp)
+alternative_if_not ARM64_HAS_VIRT_HOST_EXTN	
 	hvc	#0
 	ret
+alternative_else
+	b	__vhe_hyp_call
+	nop
+alternative_endif
 ENDPROC(kvm_call_hyp)

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.

quoted

+	mov	lr, x0
+	mov	x0, x1
+	mov	x1, x2
+	mov	x2, x3
+	blr	lr
+	ldp	lr, xzr, [sp], #16
+.endm
+
+ENTRY(__vhe_hyp_call)
+	do_el2_call
+	/*
+	 * We used to rely on having an exception return to get
+	 * an implicit isb. In the E2H case, we don't have it anymore.
+	 * rather than changing all the leaf functions, just do it here
+	 * before returning to the rest of the kernel.
+	 */

why is this not the case with an ISB before do_el2_call then?

That's a good point. I guess the safest thing to do would be to add one,
but looking at the various functions we call, I don't see any that could
go wrong by not having a ISB in their prologue.

Or maybe you've identified such a case?

Thanks,

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