Ashwin, Marc,
On 12/03/2015 10:58 PM, Marc Zyngier wrote:
> On 02/12/15 22:40, Ashwin Chaugule wrote:
>> Hello,
>>
>> On 24 November 2015 at 17:25, Geoff Levand <geoff at infradead.org> wrote:
>>> From: AKASHI Takahiro <takahiro.akashi at linaro.org>
>>>
>>> The current kvm implementation on arm64 does cpu-specific initialization
>>> at system boot, and has no way to gracefully shutdown a core in terms of
>>> kvm. This prevents, especially, kexec from rebooting the system on a boot
>>> core in EL2.
>>>
>>> This patch adds a cpu tear-down function and also puts an existing cpu-init
>>> code into a separate function, kvm_arch_hardware_disable() and
>>> kvm_arch_hardware_enable() respectively.
>>> We don't need arm64-specific cpu hotplug hook any more.
>>>
>>> Since this patch modifies common part of code between arm and arm64, one
>>> stub definition, __cpu_reset_hyp_mode(), is added on arm side to avoid
>>> compiling errors.
>>>
>>> Signed-off-by: AKASHI Takahiro <takahiro.akashi at linaro.org>
>>> ---
>>> arch/arm/include/asm/kvm_host.h | 10 ++++-
>>> arch/arm/include/asm/kvm_mmu.h | 1 +
>>> arch/arm/kvm/arm.c | 79 ++++++++++++++++++---------------------
>>> arch/arm/kvm/mmu.c | 5 +++
>>> arch/arm64/include/asm/kvm_host.h | 16 +++++++-
>>> arch/arm64/include/asm/kvm_mmu.h | 1 +
>>> arch/arm64/include/asm/virt.h | 9 +++++
>>> arch/arm64/kvm/hyp-init.S | 33 ++++++++++++++++
>>> arch/arm64/kvm/hyp.S | 32 ++++++++++++++--
>>> 9 files changed, 138 insertions(+), 48 deletions(-)
>>
>> [..]
>>
>>>
>>>
>>> static struct notifier_block hyp_init_cpu_pm_nb = {
>>> @@ -1108,11 +1119,6 @@ static int init_hyp_mode(void)
>>> }
>>>
>>> /*
>>> - * Execute the init code on each CPU.
>>> - */
>>> - on_each_cpu(cpu_init_hyp_mode, NULL, 1);
>>> -
>>> - /*
>>> * Init HYP view of VGIC
>>> */
>>> err = kvm_vgic_hyp_init();
>>
>> With this flow, the cpu_init_hyp_mode() is called only at VM guest
>> creation, but vgic_hyp_init() is called at bootup. On a system with
>> GICv3, it looks like we end up with bogus values from the ICH_VTR_EL2
>> (to get the number of LRs), because we're not reading it from EL2
>> anymore.
Thank you for pointing this out.
Recently I tested my kdump code on hikey, and as hikey(hi6220) has gic-400,
I didn't notice this problem.
> Indeed, this is completely broken (I just reproduced the issue on a
> model). I wish this kind of details had been checked earlier, but thanks
> for pointing it out.
>
>> Whats the best way to fix this?
>> - Call kvm_arch_hardware_enable() before vgic_hyp_init() and disable later?
>> - Fold the VGIC init stuff back into hardware_enable()?
>
> None of that works - kvm_arch_hardware_enable() is called once per CPU,
> while vgic_hyp_init() can only be called once. Also,
> kvm_arch_hardware_enable() is called from interrupt context, and I
> wouldn't feel comfortable starting probing DT and allocating stuff from
> there.
Do you think so?
How about the fixup! patch attached below?
The point is that, like Ashwin's first idea, we initialize cpus temporarily
before kvm_vgic_hyp_init() and then soon reset cpus again. Thus,
kvm cpu hotplug will still continue to work as before.
Now that cpu_init_hyp_mode() is revived as exactly the same as Marc's
original code, the change will not be a big jump.
If kvm_hyp_call() in vgic_v3_probe()/kvm_vgic_hyp_init() is a *problem*,
I hope this should work. Actually I confirmed that, with this fixup! patch,
we could run a kvm guest and also successfully executed kexec on model w/gic-v3.
My only concern is the following kernel message I saw when kexec shut down
the kernel:
(Please note that I was running one kvm quest (pid=961) here.)
===
sh-4.3# ./kexec -d -e
kexec version: 15.11.16.11.06-g41e52e2
arch_process_options:112: command_line: (null)
arch_process_options:114: initrd: (null)
arch_process_options:115: dtb: (null)
arch_process_options:117: port: 0x0
kvm: exiting hardware virtualization
kvm [961]: Unsupported exception type: 6248304 <== this message
kexec_core: Starting new kernel
Disabling non-boot CPUs ...
CPU1: shutdown
CPU2: shutdown
CPU3: shutdown
CPU4: shutdown
CPU5: shutdown
CPU6: shutdown
CPU7: shutdown
Bye!
Booting Linux on physical CPU 0x0
...
===
I don't know whether we can ignore this kind of message or not.
Any thoughts?
Thanks,
-Takahiro AKASHI
>> - Read the VGIC number of LRs from the hyp stub?
>
> That's may UNDEF if called in the wrong context. Also, this defeats the
> point of stubs, which is just to install the vectors for the hypervisor.
>
>> - ..
>
> Yeah, quite.
>
> Geoff, Takahiro?
>
> M.
>
----8<----
From 66ca3baedf45c78c81a76ea77ddd6ace49550ab6 Mon Sep 17 00:00:00 2001
From: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx>
Date: Fri, 11 Dec 2015 13:43:35 +0900
Subject: [PATCH 7/7] fixup! arm64: kvm: allows kvm cpu hotplug
---
arch/arm/kvm/arm.c | 37 +++++++++++++++++++++++++++----------
1 file changed, 27 insertions(+), 10 deletions(-)
diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
index 518c3c7..8fe59ba 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -950,7 +950,7 @@ long kvm_arch_vm_ioctl(struct file *filp,
}
}
-int kvm_arch_hardware_enable(void)
+static void cpu_init_hyp_mode(void *dummy)
{
phys_addr_t boot_pgd_ptr;
phys_addr_t pgd_ptr;
@@ -958,9 +958,6 @@ int kvm_arch_hardware_enable(void)
unsigned long stack_page;
unsigned long vector_ptr;
- if (__hyp_get_vectors() != hyp_default_vectors)
- return 0;
-
/* Switch from the HYP stub to our own HYP init vector */
__hyp_set_vectors(kvm_get_idmap_vector());
@@ -973,24 +970,35 @@ int kvm_arch_hardware_enable(void)
__cpu_init_hyp_mode(boot_pgd_ptr, pgd_ptr, hyp_stack_ptr, vector_ptr);
kvm_arm_init_debug();
-
- return 0;
}
-void kvm_arch_hardware_disable(void)
+static void cpu_reset_hyp_mode(void *dummy)
{
phys_addr_t boot_pgd_ptr;
phys_addr_t phys_idmap_start;
- if (__hyp_get_vectors() == hyp_default_vectors)
- return;
-
boot_pgd_ptr = kvm_mmu_get_boot_httbr();
phys_idmap_start = kvm_get_idmap_start();
__cpu_reset_hyp_mode(boot_pgd_ptr, phys_idmap_start);
}
+int kvm_arch_hardware_enable(void)
+{
+ if (__hyp_get_vectors() == hyp_default_vectors)
+ cpu_init_hyp_mode(NULL);
+
+ return 0;
+}
+
+void kvm_arch_hardware_disable(void)
+{
+ if (__hyp_get_vectors() == hyp_default_vectors)
+ return;
+
+ cpu_reset_hyp_mode(NULL);
+}
+
#ifdef CONFIG_CPU_PM
static int hyp_init_cpu_pm_notifier(struct notifier_block *self,
unsigned long cmd,
@@ -1114,6 +1122,12 @@ static int init_hyp_mode(void)
}
/*
+ * Execute the init code on each CPU.
+ * Only needed to execute kvm_hyp_call() during *_hyp_init().
+ */
+ on_each_cpu(cpu_init_hyp_mode, NULL, 1);
+
+ /*
* Init HYP view of VGIC
*/
err = kvm_vgic_hyp_init();
@@ -1127,6 +1141,8 @@ static int init_hyp_mode(void)
if (err)
goto out_free_context;
+ on_each_cpu(cpu_reset_hyp_mode, NULL, 1);
+
#ifndef CONFIG_HOTPLUG_CPU
free_boot_hyp_pgd();
#endif
@@ -1137,6 +1153,7 @@ static int init_hyp_mode(void)
return 0;
out_free_context:
+ on_each_cpu(cpu_reset_hyp_mode, NULL, 1);
free_percpu(kvm_host_cpu_state);
out_free_mappings:
free_hyp_pgds();
--
1.7.9.5
