linux-kernel - [PATCH v6 04/21] arm64: Provide an 'upgrade to VHE' stub hypercall

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Message-Id: <20210201115637.3123740-5-maz@kernel.org>
Date:   Mon,  1 Feb 2021 11:56:20 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        David Brazdil <dbrazdil@...gle.com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Jing Zhang <jingzhangos@...gle.com>,
        Ajay Patil <pajay@....qualcomm.com>,
        Prasad Sodagudi <psodagud@...eaurora.org>,
        Srinivas Ramana <sramana@...eaurora.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        kernel-team@...roid.com
Subject: [PATCH v6 04/21] arm64: Provide an 'upgrade to VHE' stub hypercall

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@...nel.org>
Acked-by: David Brazdil <dbrazdil@...gle.com>
Acked-by: Catalin Marinas <catalin.marinas@....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