Re: [PATCH stable v5.4+ 1/3] x86/kvm: Teardown PV features on boot CPU as well

[Paolo Bonzini <pbonzini@redhat.com>]

On 20/05/21 14:56, Krzysztof Kozlowski wrote:
> From: Vitaly Kuznetsov <vkuznets@redhat.com>
> 
> commit 8b79feffeca28c5459458fe78676b081e87c93a4 upstream.
> 
> Various PV features (Async PF, PV EOI, steal time) work through memory
> shared with hypervisor and when we restore from hibernation we must
> properly teardown all these features to make sure hypervisor doesn't
> write to stale locations after we jump to the previously hibernated kernel
> (which can try to place anything there). For secondary CPUs the job is
> already done by kvm_cpu_down_prepare(), register syscore ops to do
> the same for boot CPU.
> 
> Krzysztof:
> This fixes memory corruption visible after second resume from
> hibernation:

Hi, you should include a cover letter detailing the differences between 
the original patches and the backport.

(I'll review it anyway, but it would have helped).

Paolo

>    BUG: Bad page state in process dbus-daemon  pfn:18b01
>    page:ffffea000062c040 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 compound_mapcount: -30591
>    flags: 0xfffffc0078141(locked|error|workingset|writeback|head|mappedtodisk|reclaim)
>    raw: 000fffffc0078141 dead0000000002d0 dead000000000100 0000000000000000
>    raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
>    page dumped because: PAGE_FLAGS_CHECK_AT_PREP flag set
>    bad because of flags: 0x78141(locked|error|workingset|writeback|head|mappedtodisk|reclaim)
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> Message-Id: <20210414123544.1060604-3-vkuznets@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
> [krzysztof: Extend the commit message]
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
> ---
> 
> Backport to v5.4 seems reasonable. Might have sense to earlier versions,
> but this was not tested/investigated.
> 
>   arch/x86/kernel/kvm.c | 32 ++++++++++++++++++++++++++++----
>   1 file changed, 28 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index e820568ed4d5..6b906a651fb1 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -24,6 +24,7 @@
>   #include <linux/debugfs.h>
>   #include <linux/nmi.h>
>   #include <linux/swait.h>
> +#include <linux/syscore_ops.h>
>   #include <asm/timer.h>
>   #include <asm/cpu.h>
>   #include <asm/traps.h>
> @@ -558,17 +559,21 @@ static void kvm_guest_cpu_offline(void)
>   
>   static int kvm_cpu_online(unsigned int cpu)
>   {
> -	local_irq_disable();
> +	unsigned long flags;
> +
> +	local_irq_save(flags);
>   	kvm_guest_cpu_init();
> -	local_irq_enable();
> +	local_irq_restore(flags);
>   	return 0;
>   }
>   
>   static int kvm_cpu_down_prepare(unsigned int cpu)
>   {
> -	local_irq_disable();
> +	unsigned long flags;
> +
> +	local_irq_save(flags);
>   	kvm_guest_cpu_offline();
> -	local_irq_enable();
> +	local_irq_restore(flags);
>   	return 0;
>   }
>   #endif
> @@ -606,6 +611,23 @@ static void kvm_flush_tlb_others(const struct cpumask *cpumask,
>   	native_flush_tlb_others(flushmask, info);
>   }
>   
> +static int kvm_suspend(void)
> +{
> +	kvm_guest_cpu_offline();
> +
> +	return 0;
> +}
> +
> +static void kvm_resume(void)
> +{
> +	kvm_cpu_online(raw_smp_processor_id());
> +}
> +
> +static struct syscore_ops kvm_syscore_ops = {
> +	.suspend	= kvm_suspend,
> +	.resume		= kvm_resume,
> +};
> +
>   static void __init kvm_guest_init(void)
>   {
>   	int i;
> @@ -649,6 +671,8 @@ static void __init kvm_guest_init(void)
>   	kvm_guest_cpu_init();
>   #endif
>   
> +	register_syscore_ops(&kvm_syscore_ops);
> +
>   	/*
>   	 * Hard lockup detection is enabled by default. Disable it, as guests
>   	 * can get false positives too easily, for example if the host is
>