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Subject[PATCH v7 04/23] arm64: Provide an 'upgrade to VHE' stub hypercall
Date
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>
Acked-by: David Brazdil <dbrazdil@google.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
---
arch/arm64/include/asm/virt.h | 7 +++-
arch/arm64/kernel/hyp-stub.S | 76 ++++++++++++++++++++++++++++++++++-
2 files changed, 80 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..3f3dbbe8914d 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 +73,75 @@ 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)
+ // Be prepared to fail
+ mov_q x0, HVC_STUB_ERR
+
+ // Sanity check: MMU *must* be off
+ mrs x1, sctlr_el2
+ tbnz x1, #0, 1f
+
+ // Needs to be VHE capable, obviously
+ mrs x1, id_aa64mmfr1_el1
+ ubfx x1, x1, #ID_AA64MMFR1_VHE_SHIFT, #4
+ cbz x1, 1f
+
+ // Engage the VHE magic!
+ mov_q x0, HCR_HOST_VHE_FLAGS
+ msr hcr_el2, x0
+ isb
+
+ // Doesn't do much on VHE, but still, worth a shot
+ init_el2_state vhe
+
+ // Use the EL1 allocated stack, per-cpu offset
+ mrs x0, sp_el1
+ mov sp, x0
+ mrs x0, tpidr_el1
+ msr tpidr_el2, x0
+
+ // FP configuration, vectors
+ mrs_s x0, SYS_CPACR_EL12
+ msr cpacr_el1, x0
+ mrs_s x0, SYS_VBAR_EL12
+ msr vbar_el1, x0
+
+ // Transfer the MM state from EL1 to EL2
+ mrs_s x0, SYS_TCR_EL12
+ msr tcr_el1, x0
+ mrs_s x0, SYS_TTBR0_EL12
+ msr ttbr0_el1, x0
+ mrs_s x0, SYS_TTBR1_EL12
+ msr ttbr1_el1, x0
+ mrs_s x0, SYS_MAIR_EL12
+ msr mair_el1, x0
+ isb
+
+ // Invalidate TLBs before enabling the MMU
+ tlbi vmalle1
+ dsb nsh
+
+ // Enable the EL2 S1 MMU, as set up from EL1
+ mrs_s x0, SYS_SCTLR_EL12
+ set_sctlr_el1 x0
+
+ // Disable the EL1 S1 MMU for a good measure
+ mov_q x0, INIT_SCTLR_EL1_MMU_OFF
+ msr_s SYS_SCTLR_EL12, x0
+
+ // Hack the exception return to stay at EL2
+ mrs x0, spsr_el1
+ and x0, x0, #~PSR_MODE_MASK
+ mov x1, #PSR_MODE_EL2h
+ orr x0, x0, x1
+ msr spsr_el1, x0
+
+ mov x0, xzr
+
+1: eret
+SYM_CODE_END(mutate_to_vhe)
+
.macro invalid_vector label
SYM_CODE_START_LOCAL(\label)
b \label
--
2.29.2
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