Re: [PATCH v3 03/41] KVM: arm64: Avoid storing the vcpu pointer on the stack

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Hi Christoffer,

On 12/01/18 12:07, Christoffer Dall wrote:
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 048f5db120f3..6ce0b428a4db 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -350,10 +350,15 @@ int kvm_perf_teardown(void);
struct kvm_vcpu *kvm_mpidr_to_vcpu(struct kvm *kvm, unsigned long mpidr); +extern void __kvm_set_tpidr_el2(u64 tpidr_el2);

NIT: The rest of the file seem to declare prototype without extern.

[...]

diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index 71bf088f1e4b..612021dce84f 100644
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -135,6 +135,7 @@ int main(void)
    DEFINE(CPU_FP_REGS,		offsetof(struct kvm_regs, fp_regs));
    DEFINE(VCPU_FPEXC32_EL2,	offsetof(struct kvm_vcpu, arch.ctxt.sys_regs[FPEXC32_EL2]));
    DEFINE(VCPU_HOST_CONTEXT,	offsetof(struct kvm_vcpu, arch.host_cpu_context));
+  DEFINE(HOST_CONTEXT_VCPU,	offsetof(struct kvm_cpu_context, __hyp_running_vcpu));
  #endif
  #ifdef CONFIG_CPU_PM
    DEFINE(CPU_SUSPEND_SZ,	sizeof(struct cpu_suspend_ctx));
diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
index 9a8ab5dddd9e..a360ac6e89e9 100644
--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S
@@ -62,9 +62,6 @@ ENTRY(__guest_enter)
  	// Store the host regs
  	save_callee_saved_regs x1
- // Store host_ctxt and vcpu for use at exit time
-	stp	x1, x0, [sp, #-16]!
-
  	add	x18, x0, #VCPU_CONTEXT
// Restore guest regs x0-x17
@@ -118,8 +115,7 @@ ENTRY(__guest_exit)
  	// Store the guest regs x19-x29, lr
  	save_callee_saved_regs x1
- // Restore the host_ctxt from the stack
-	ldr	x2, [sp], #16
+	get_host_ctxt	x2, x3
// Now restore the host regs
  	restore_callee_saved_regs x2
diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
index e4f37b9dd47c..71b4cc92895e 100644
--- a/arch/arm64/kvm/hyp/hyp-entry.S
+++ b/arch/arm64/kvm/hyp/hyp-entry.S
@@ -56,18 +56,15 @@ ENDPROC(__vhe_hyp_call)
  el1_sync:				// Guest trapped into EL2
  	stp	x0, x1, [sp, #-16]!
-alternative_if_not ARM64_HAS_VIRT_HOST_EXTN
-	mrs	x1, esr_el2
-alternative_else
-	mrs	x1, esr_el1
-alternative_endif
-	lsr	x0, x1, #ESR_ELx_EC_SHIFT
+	mrs	x1, vttbr_el2		// If vttbr is valid, this is a trap
+	cbnz	x1, el1_trap		// from the guest
- cmp x0, #ESR_ELx_EC_HVC64
-	b.ne	el1_trap
-
-	mrs	x1, vttbr_el2		// If vttbr is valid, the 64bit guest
-	cbnz	x1, el1_trap		// called HVC
+#ifdef CONFIG_DEBUG
+	mrs	x0, esr_el2
+	lsr	x0, x0, #ESR_ELx_EC_SHIFT
+	cmp     x0, #ESR_ELx_EC_HVC64
+	b.ne    __hyp_panic
+#endif

FWIW, I noticed that Mark's series about Spectre is also touching this code (see https://patchwork.kernel.org/patch/10190297/).

Cheers,

--
Julien Grall
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