On Mon, 18 Jan 2021 11:25:16 +0000,
David Brazdil [off-list ref] wrote:

On Mon, Jan 18, 2021 at 09:45:16AM +0000, Marc Zyngier wrote:

quoted

As we are about to change the way a VHE system boots, let's
provide the core helper, in the form of a stub hypercall that
enables VHE and replicates the full EL1 context at EL2, thanks
to EL1 and VHE-EL2 being extremely similar.

On exception return, the kernel carries on at EL2. Fancy!

Nothing calls this new hypercall yet, so no functional change.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/include/asm/virt.h |  7 +++-
 arch/arm64/kernel/hyp-stub.S  | 67 +++++++++++++++++++++++++++++++++--
 2 files changed, 71 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
index ee6a48df89d9..7379f35ae2c6 100644
--- a/arch/arm64/include/asm/virt.h
+++ b/arch/arm64/include/asm/virt.h

@@ -35,8 +35,13 @@
  */
 #define HVC_RESET_VECTORS 2
 
+/*
+ * HVC_VHE_RESTART - Upgrade the CPU from EL1 to EL2, if possible
+ */
+#define HVC_VHE_RESTART	3
+
 /* Max number of HYP stub hypercalls */
-#define HVC_STUB_HCALL_NR 3
+#define HVC_STUB_HCALL_NR 4
 
 /* Error returned when an invalid stub number is passed into x0 */
 #define HVC_STUB_ERR	0xbadca11

diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S
index 160f5881a0b7..fb12398b5c28 100644
--- a/arch/arm64/kernel/hyp-stub.S
+++ b/arch/arm64/kernel/hyp-stub.S

@@ -8,9 +8,9 @@
 
 #include <linux/init.h>
 #include <linux/linkage.h>
-#include <linux/irqchip/arm-gic-v3.h>
 
 #include <asm/assembler.h>
+#include <asm/el2_setup.h>
 #include <asm/kvm_arm.h>
 #include <asm/kvm_asm.h>
 #include <asm/ptrace.h>

@@ -47,10 +47,13 @@ SYM_CODE_END(__hyp_stub_vectors)
 
 SYM_CODE_START_LOCAL(el1_sync)
 	cmp	x0, #HVC_SET_VECTORS
-	b.ne	2f
+	b.ne	1f
 	msr	vbar_el2, x1
 	b	9f
 
+1:	cmp	x0, #HVC_VHE_RESTART
+	b.eq	mutate_to_vhe
+
 2:	cmp	x0, #HVC_SOFT_RESTART
 	b.ne	3f
 	mov	x0, x2

@@ -70,6 +73,66 @@ SYM_CODE_START_LOCAL(el1_sync)
 	eret
 SYM_CODE_END(el1_sync)
 
+// nVHE? No way! Give me the real thing!
+SYM_CODE_START_LOCAL(mutate_to_vhe)
+	// Sanity check: MMU *must* be off
+	mrs	x0, sctlr_el2
+	tbnz	x0, #0, 1f
+
+	// Needs to be VHE capable, obviously
+	mrs	x0, id_aa64mmfr1_el1
+	ubfx	x0, x0, #ID_AA64MMFR1_VHE_SHIFT, #4
+	cbz	x0, 1f

nit: There is a HVC_STUB_ERR that you could return if these sanity
checks fail.  The documentation also states that it should be
returned on error.

Good point. I've now added it, but how the error can be handled is
still up in the air. For now, I've decided to let the kernel continue
its (probably doomed) course.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

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