[PATCH v7 07/16] arm64: kvm: allows kvm cpu hotplug
AKASHI Takahiro
takahiro.akashi at linaro.org
Mon Apr 25 01:41:11 PDT 2016
On Wed, Apr 20, 2016 at 12:19:45PM +0100, James Morse wrote:
> Hi Marc,
>
> On 20/04/16 11:37, Marc Zyngier wrote:
> > On 19/04/16 18:37, James Morse wrote:
> >> It looks like x86 uses the extable to work around this, their vmx_vcpu_run() has:
> >>> __ex(ASM_VMX_VMLAUNCH) "\n\t"
> >> Where __ex ends up calling ____kvm_handle_fault_on_reboot(), with a nearby comment:
> >>> * Hardware virtualization extension instructions may fault if a
> >>> * reboot turns off virtualization while processes are running.
> >>> * Trap the fault and ignore the instruction if that happens.
> >
> > I very much like that approach, to be honest. Tearing down a CPU is
> > something exceptional, so let's make it an actual exception.
> >
> > It is now pretty easy to discriminate between KVM functions and stub
> > functions thanks to your earlier patch, so if we end up calling the
> > hyp-stub because we've torn down KVM's EL2, let's just return an
> > appropriate error code (ARM_EXCEPTION_HYP_GONE), and handle it at EL1.
>
> Okay. kexec uses kvm_call_hyp() against the hyp-stub to do the kernel-copy and
> hand over to purgatory, but we could change that to a new 'special' builtin
> call, something like HVC_KEXEC_CALL_HYP. It never calls it with kvm loaded, so
> there is no reason the calls have to be same.
>
> Given hibernate doesn't hit this issue, I will drop this hunk from this version
> of the patch, and repost hibernate incorporating the feedback so far. I will
> provide a patch for kexec to do the above.
Thanks, but you don' have to.
If the fix below is acceptable, we will merge it to our next kexec/kdump
patch series.
-Takahiro AKASHI
> Thanks,
>
> James
>From d70cf5d3202d819bd7f8c9072c61da783bf07b40 Mon Sep 17 00:00:00 2001
From: AKASHI Takahiro <takahiro.akashi at linaro.org>
Date: Mon, 25 Apr 2016 17:29:55 +0900
Subject: [PATCH] arm64: kvm: (experimental) fix kexec exception due to kexec
reoot
---
arch/arm/kvm/arm.c | 8 +-------
arch/arm64/include/asm/kvm_asm.h | 1 +
arch/arm64/include/asm/virt.h | 5 +++++
arch/arm64/kernel/cpu-reset.S | 5 +----
arch/arm64/kernel/hyp-stub.S | 14 ++++++++++++--
arch/arm64/kvm/handle_exit.c | 4 ++++
6 files changed, 24 insertions(+), 13 deletions(-)
diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
index 962904a..0e92787 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -587,13 +587,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
/*
* Re-check atomic conditions
*/
- if (unlikely(!__this_cpu_read(kvm_arm_hardware_enabled))) {
- /* cpu has been torn down */
- ret = 0;
- run->exit_reason = KVM_EXIT_FAIL_ENTRY;
- run->fail_entry.hardware_entry_failure_reason
- = (u64)-ENOEXEC;
- } else if (signal_pending(current)) {
+ if (signal_pending(current)) {
ret = -EINTR;
run->exit_reason = KVM_EXIT_INTR;
}
diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index ebc8d0e..7f653ad 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -22,6 +22,7 @@
#define ARM_EXCEPTION_IRQ 0
#define ARM_EXCEPTION_TRAP 1
+#define ARM_EXCEPTION_HYP_GONE 2
#define KVM_ARM64_DEBUG_DIRTY_SHIFT 0
#define KVM_ARM64_DEBUG_DIRTY (1 << KVM_ARM64_DEBUG_DIRTY_SHIFT)
diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
index d406d2e..9079661 100644
--- a/arch/arm64/include/asm/virt.h
+++ b/arch/arm64/include/asm/virt.h
@@ -34,6 +34,11 @@
*/
#define HVC_SET_VECTORS 1
+/*
+ * HVC_KEXEC_RESTART
+ */
+#define HVC_KEXEC_RESTART 2
+
#define BOOT_CPU_MODE_EL1 (0xe11)
#define BOOT_CPU_MODE_EL2 (0xe12)
diff --git a/arch/arm64/kernel/cpu-reset.S b/arch/arm64/kernel/cpu-reset.S
index 11a5bc6..4d35331 100644
--- a/arch/arm64/kernel/cpu-reset.S
+++ b/arch/arm64/kernel/cpu-reset.S
@@ -41,10 +41,7 @@ ENTRY(__cpu_soft_restart)
isb
cbz x0, 1f // el2_switch?
- mov x0, x1 // entry
- mov x1, x2 // arg0
- mov x2, x3 // arg1
- mov x3, x4 // arg2
+ mov x0, #HVC_KEXEC_RESTART
hvc #0 // no return
1: mov x18, x1 // entry
diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S
index 6bba25c..7fad129 100644
--- a/arch/arm64/kernel/hyp-stub.S
+++ b/arch/arm64/kernel/hyp-stub.S
@@ -22,7 +22,8 @@
#include <linux/irqchip/arm-gic-v3.h>
#include <asm/assembler.h>
-#include <asm/kvm_arm.h>
+#include <asm/esr.h>
+#include <asm/kvm_asm.h>
#include <asm/ptrace.h>
#include <asm/virt.h>
@@ -70,7 +71,16 @@ el1_sync:
msr vbar_el2, x1
b 9f
-2: do_el2_call
+2: cmp x0, #HVC_KEXEC_RESTART
+ b.eq 3f
+ mov x0, #ARM_EXCEPTION_HYP_GONE
+ b 9f
+
+3: mov lr, x1
+ mov x0, x2
+ mov x1, x3
+ mov x2, x4
+ blr lr
9: eret
ENDPROC(el1_sync)
diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index eba89e4..31b5224 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -186,6 +186,10 @@ int handle_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
exit_handler = kvm_get_exit_handler(vcpu);
return exit_handler(vcpu, run);
+ case ARM_EXCEPTION_HYP_GONE:
+ /* due to kexec reboot */
+ run->exit_reason = KVM_EXIT_SHUTDOWN;
+ return 0;
default:
kvm_pr_unimpl("Unsupported exception type: %d",
exception_index);
--
2.8.1
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