linux-kernel - [RFC PATCH 5/6] kvm: arm64: Fix constant-pool users in hyp

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Date:   Thu, 19 Nov 2020 16:25:42 +0000
From:   David Brazdil <dbrazdil@...gle.com>
To:     kvmarm@...ts.cs.columbia.edu
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Andrew Scull <ascull@...gle.com>,
        Ard Biesheuvel <ardb@...nel.org>, kernel-team@...roid.com,
        David Brazdil <dbrazdil@...gle.com>
Subject: [RFC PATCH 5/6] kvm: arm64: Fix constant-pool users in hyp

Hyp code used to use absolute addressing via a constant pool to obtain
the kernel VA of 3 symbols - panic, __hyp_panic_string and
__kvm_handle_stub_hvc. This used to work because the kernel would
relocate the addresses in the constant pool to kernel VA at boot and hyp
would simply load them from there.

Now that relocations are fixed up to point to hyp VAs, this does not
work any longer. Rework the helpers to convert hyp VA to kernel VA / PA
as needed.

Signed-off-by: David Brazdil <dbrazdil@...gle.com>
---
 arch/arm64/include/asm/kvm_mmu.h | 29 +++++++++++++++++++----------
 arch/arm64/kvm/hyp/nvhe/host.S   | 29 +++++++++++++++--------------
 2 files changed, 34 insertions(+), 24 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index 8cb8974ec9cc..0676ff2105bb 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -72,9 +72,14 @@ alternative_cb kvm_update_va_mask
 alternative_cb_end
 .endm
 
+.macro hyp_pa reg, tmp
+	ldr_l	\tmp, hyp_physvirt_offset
+	add	\reg, \reg, \tmp
+.endm
+
 /*
- * Convert a kernel image address to a PA
- * reg: kernel address to be converted in place
+ * Convert a hypervisor VA to a kernel image address
+ * reg: hypervisor address to be converted in place
  * tmp: temporary register
  *
  * The actual code generation takes place in kvm_get_kimage_voffset, and
@@ -82,18 +87,22 @@ alternative_cb_end
  * perform the register allocation (kvm_get_kimage_voffset uses the
  * specific registers encoded in the instructions).
  */
-.macro kimg_pa reg, tmp
+.macro hyp_kimg reg, tmp
+	/* Convert hyp VA -> PA. */
+	hyp_pa	\reg, \tmp
+
+	/* Load kimage_voffset. */
 alternative_cb kvm_get_kimage_voffset
-       movz    \tmp, #0
-       movk    \tmp, #0, lsl #16
-       movk    \tmp, #0, lsl #32
-       movk    \tmp, #0, lsl #48
+	movz	\tmp, #0
+	movk	\tmp, #0, lsl #16
+	movk	\tmp, #0, lsl #32
+	movk	\tmp, #0, lsl #48
 alternative_cb_end
 
-       /* reg = __pa(reg) */
-       sub     \reg, \reg, \tmp
+	/* Convert PA -> kimg VA. */
+	add	\reg, \reg, \tmp
 .endm
-	 
+
 #else
 
 #include <linux/pgtable.h>
diff --git a/arch/arm64/kvm/hyp/nvhe/host.S b/arch/arm64/kvm/hyp/nvhe/host.S
index 596dd5ae8e77..bcb80d525d8c 100644
--- a/arch/arm64/kvm/hyp/nvhe/host.S
+++ b/arch/arm64/kvm/hyp/nvhe/host.S
@@ -74,27 +74,28 @@ SYM_FUNC_END(__host_enter)
  * void __noreturn __hyp_do_panic(bool restore_host, u64 spsr, u64 elr, u64 par);
  */
 SYM_FUNC_START(__hyp_do_panic)
-	/* Load the format arguments into x1-7 */
-	mov	x6, x3
-	get_vcpu_ptr x7, x3
-
-	mrs	x3, esr_el2
-	mrs	x4, far_el2
-	mrs	x5, hpfar_el2
-
 	/* Prepare and exit to the host's panic funciton. */
 	mov	lr, #(PSR_F_BIT | PSR_I_BIT | PSR_A_BIT | PSR_D_BIT |\
 		      PSR_MODE_EL1h)
 	msr	spsr_el2, lr
 	ldr	lr, =panic
+	hyp_kimg lr, x6
 	msr	elr_el2, lr
 
-	/*
-	 * Set the panic format string and enter the host, conditionally
-	 * restoring the host context.
-	 */
+	/* Set the panic format string. Use the, now free, LR as scratch. */
+	ldr	lr, =__hyp_panic_string
+	hyp_kimg lr, x6
+
+	/* Load the format arguments into x1-7. */
+	mov	x6, x3
+	get_vcpu_ptr x7, x3
+	mrs	x3, esr_el2
+	mrs	x4, far_el2
+	mrs	x5, hpfar_el2
+
+	/* Enter the host, conditionally restoring the host context. */
 	cmp	x0, xzr
-	ldr	x0, =__hyp_panic_string
+	mov	x0, lr
 	b.eq	__host_enter_without_restoring
 	b	__host_enter_for_panic
 SYM_FUNC_END(__hyp_do_panic)
@@ -124,7 +125,7 @@ SYM_FUNC_END(__hyp_do_panic)
 	 * Preserve x0-x4, which may contain stub parameters.
 	 */
 	ldr	x5, =__kvm_handle_stub_hvc
-	kimg_pa x5, x6
+	hyp_pa	x5, x6
 	br	x5
 .L__vect_end\@:
 .if ((.L__vect_end\@ - .L__vect_start\@) > 0x80)
-- 
2.29.2.299.gdc1121823c-goog