linux-kernel - [PATCH 4.9 44/66] KVM: arm64: Store vcpu on the stack during __guest

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Message-Id: <20180720121409.781488694@linuxfoundation.org>
Date:   Fri, 20 Jul 2018 14:14:01 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        James Morse <james.morse@....com>,
        Christoffer Dall <cdall@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Marc Zyngier <marc.zyngier@....com>
Subject: [PATCH 4.9 44/66] KVM: arm64: Store vcpu on the stack during __guest_enter()

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: James Morse <james.morse@....com>

Commit 32b03d1059667a39e089c45ee38ec9c16332430f upstream.

KVM uses tpidr_el2 as its private vcpu register, which makes sense for
non-vhe world switch as only KVM can access this register. This means
vhe Linux has to use tpidr_el1, which KVM has to save/restore as part
of the host context.

If the SDEI handler code runs behind KVMs back, it mustn't access any
per-cpu variables. To allow this on systems with vhe we need to make
the host use tpidr_el2, saving KVM from save/restoring it.

__guest_enter() stores the host_ctxt on the stack, do the same with
the vcpu.

Signed-off-by: James Morse <james.morse@....com>
Reviewed-by: Christoffer Dall <cdall@...aro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Marc Zyngier <marc.zyngier@....com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/arm64/kvm/hyp/entry.S     |   10 +++++++---
 arch/arm64/kvm/hyp/hyp-entry.S |    6 +++---
 2 files changed, 10 insertions(+), 6 deletions(-)

--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S
@@ -62,8 +62,8 @@ ENTRY(__guest_enter)
 	// Store the host regs
 	save_callee_saved_regs x1
 
-	// Store the host_ctxt for use at exit time
-	str	x1, [sp, #-16]!
+	// Store host_ctxt and vcpu for use at exit time
+	stp	x1, x0, [sp, #-16]!
 
 	add	x18, x0, #VCPU_CONTEXT
 
@@ -159,6 +159,10 @@ abort_guest_exit_end:
 ENDPROC(__guest_exit)
 
 ENTRY(__fpsimd_guest_restore)
+	// x0: esr
+	// x1: vcpu
+	// x2-x29,lr: vcpu regs
+	// vcpu x0-x1 on the stack
 	stp	x2, x3, [sp, #-16]!
 	stp	x4, lr, [sp, #-16]!
 
@@ -173,7 +177,7 @@ alternative_else
 alternative_endif
 	isb
 
-	mrs	x3, tpidr_el2
+	mov	x3, x1
 
 	ldr	x0, [x3, #VCPU_HOST_CONTEXT]
 	kern_hyp_va x0
--- a/arch/arm64/kvm/hyp/hyp-entry.S
+++ b/arch/arm64/kvm/hyp/hyp-entry.S
@@ -121,24 +121,24 @@ el1_trap:
 	/*
 	 * x0: ESR_EC
 	 */
+	ldr	x1, [sp, #16 + 8]	// vcpu stored by __guest_enter
 
 	/* Guest accessed VFP/SIMD registers, save host, restore Guest */
 	cmp	x0, #ESR_ELx_EC_FP_ASIMD
 	b.eq	__fpsimd_guest_restore
 
-	mrs	x1, tpidr_el2
 	mov	x0, #ARM_EXCEPTION_TRAP
 	b	__guest_exit
 
 el1_irq:
 	stp     x0, x1, [sp, #-16]!
-	mrs	x1, tpidr_el2
+	ldr	x1, [sp, #16 + 8]
 	mov	x0, #ARM_EXCEPTION_IRQ
 	b	__guest_exit
 
 el1_error:
 	stp     x0, x1, [sp, #-16]!
-	mrs	x1, tpidr_el2
+	ldr	x1, [sp, #16 + 8]
 	mov	x0, #ARM_EXCEPTION_EL1_SERROR
 	b	__guest_exit