Re: [PATCH 7/8] arm64/kexec: Add checks for KVM

From: AKASHI Takahiro <takahiro.akashi@linaro.org>
To: Mark Rutland <mark.rutland@arm.com>, Geoff Levand <geoff@infradead.org>
Cc: Marc Zyngier <Marc.Zyngier@arm.com>,
	Catalin Marinas <Catalin.Marinas@arm.com>,
	Will Deacon <Will.Deacon@arm.com>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"grant.likely@linaro.org" <grant.likely@linaro.org>,
	"kexec@lists.infradead.org" <kexec@lists.infradead.org>,
	"christoffer.dall@linaro.org" <christoffer.dall@linaro.org>
Subject: Re: [PATCH 7/8] arm64/kexec: Add checks for KVM
Date: Thu, 29 Jan 2015 18:57:48 +0900	[thread overview]
Message-ID: <54CA041C.6020403@linaro.org> (raw)
In-Reply-To: <20150126191942.GQ23313@leverpostej>

Hello,

On 01/27/2015 04:19 AM, Mark Rutland wrote:
> On Sat, Jan 17, 2015 at 12:23:34AM +0000, Geoff Levand wrote:
>> Add runtime checks that fail the arm64 kexec syscall for situations that would
>> result in system instability do to problems in the KVM kernel support.
>> These checks should be removed when the KVM problems are resolved fixed.
>>
>> Signed-off-by: Geoff Levand <geoff@infradead.org>
>> ---
>>   arch/arm64/kernel/machine_kexec.c | 10 ++++++++++
>>   1 file changed, 10 insertions(+)
>>
>> diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
>> index 3d84759..a36459d 100644
>> --- a/arch/arm64/kernel/machine_kexec.c
>> +++ b/arch/arm64/kernel/machine_kexec.c
>> @@ -16,6 +16,9 @@
>>   #include <asm/cacheflush.h>
>>   #include <asm/system_misc.h>
>>
>> +/* TODO: Remove this include when KVM can support a kexec reboot. */
>> +#include <asm/virt.h>
>> +
>>   /* Global variables for the relocate_kernel routine. */
>>   extern const unsigned char relocate_new_kernel[];
>>   extern const unsigned long relocate_new_kernel_size;
>> @@ -100,6 +103,13 @@ int machine_kexec_prepare(struct kimage *image)
>>
>>   	kexec_image_info(image);
>>
>> +	/* TODO: Remove this message when KVM can support a kexec reboot. */
>> +	if (IS_ENABLED(CONFIG_KVM) && is_hyp_mode_available()) {
>> +		pr_err("%s: Your kernel is configured with KVM support (CONFIG_KVM=y) which currently does not allow for kexec re-boot.\n",
>> +			__func__);
>> +		return -ENOSYS;
>> +	}
>
> If you really don't want to implement KVM teardown, surely this should
> be at the start of the series, so we don't have a point in the middle
> where things may explode in this case?

I'm going to fix this KVM issue (teardown) in cooperation with Geoff.

Looking into kvm init code, kvm_arch_init() in particular,
I guess that teardown function (kvm_arch_exit()) should do
   (reverting kvm_timer_hyp_init() per cpu)
- stop arch timer

   (reverting cpu_init_hyp_mode() per cpu)
- flush TLB
- jump into identical mapping (using boot_hyp_pgd?)
- disable MMU?
- restore vbar_el2 to __hyp_stub_vectors (or NULL?)

   (reverting kvm_mmu_init())
- Do we need to free page tables and a bounce(trampoline) page?

Is this good enough for safely shutting down kvm?
Do I miss anything essential, or can I skip anyhing?

I really appreciate your comments.
-Takahiro AKASHI

> Mark.
>
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>

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