Re: [PATCH v21 7/9] arm64: Block hibernate and kexec while RMM is active

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 01/10/2026 12:05, Catalin Marinas wrote:
> On Thu, Oct 01, 2026 at 09:45:53AM +0100, Suzuki K Poulose wrote:
>> RMM can be deactivated only after all delegated granules have been
>> reclaimed. If a new kernel is entered while any granules remain in the
>> Realm PAS, accesses to that memory can raise a Granule Protection Fault
>> and be fatal to the new kernel.
>>
>> Crash kexec/kdump needs separate handling. It can be supported only once
>> the crash kernel can tolerate delegated memory inherited from the primary
>> kernel. i.e., be able to read the pages safely and fixup the GPF. Until
>> then disable the kexec completely.
>>
>> Hibernate has a similar problem. The image cannot be safely saved for
>> delegated pages, as the RMM doesn't support exporting the pages.
>>
>> Disable both kexec and hiberation while the RMM is active.
> 
> I would mention that this adds a new arch_hibernation_available() hook
> called from hibernation_available(), otherwise the hibernation
> maintainers may not realise why they've been cc'ed.
> 
> Alternatively, just introduce the hook as a separate patch without any
> arch code.

I will go for this approach, adding the hook in a prep patch and then
the arm64 version with kexec changes.


> 
>> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
>> Cc: Len Brown <lenb@kernel.org>
>> Cc: Pavel Machek <pavel@kernel.org>
>> Cc: linux-pm@vger.kernel.org
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>> ---
>> Changes since v20:
>>   - Add arch_hibernation_available() hook for archs to have a say and drop the
>>     other checks.
>> Changes since v19:
>>   - New patch to disable kexec and hibernation with RMM
>> ---
>>   arch/arm64/kernel/hibernate.c     | 14 ++++++++++++++
>>   arch/arm64/kernel/machine_kexec.c | 11 +++++++++++
>>   include/linux/suspend.h           |  1 +
>>   kernel/power/hibernate.c          |  8 +++++++-
>>   4 files changed, 33 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/kernel/hibernate.c b/arch/arm64/kernel/hibernate.c
>> index 7bf1174277772..08e03d24b93a8 100644
>> --- a/arch/arm64/kernel/hibernate.c
>> +++ b/arch/arm64/kernel/hibernate.c
>> @@ -10,6 +10,8 @@
>>    * Copyright (C) 2006 Rafael J. Wysocki <rjw@sisk.pl>
>>    */
>>   #define pr_fmt(x) "hibernate: " x
>> +
>> +#include <linux/arm-rmi-cmds.h>
>>   #include <linux/cpu.h>
>>   #include <linux/kvm_host.h>
>>   #include <linux/pm.h>
>> @@ -105,6 +107,18 @@ void notrace restore_processor_state(void)
>>   {
>>   }
>>   
>> +bool arch_hibernation_available(void)
>> +{
>> +	/*
>> +	 * If we have activated the RMM, there could be pages that are
>> +	 * delegated to the RMM. Trying to save them to the image will be fatal.
>> +	 * Also, we donate pages to the RMM at activation and restoring data
>> +	 * to those pages are going to be fatal.
>> +	 * Hence, disable the hibernation when the RMM is active
>> +	 */
>> +	return !cpus_are_stuck_in_kernel() && !is_rmm_active();
>> +}
> 
> For now, I would keep is_rmm_active() only in here as not to change the
> behaviour for pKVM. "disk" would disappear from /sys/power/state with
> this patch. I think it's the correct thing to do for pKVM as well but we
> can discuss this separately once this goes in (I also think pKVM using
> cpus_are_stuck_in_kernel() is a bit of a bodge but it's a handy hook
> called in the right places).

I was in double mind about this. Yes, I agree, makes sense to deal the
pKVM case separately.


> 
>> +
>>   int arch_hibernation_header_save(void *addr, unsigned int max_size)
>>   {
>>   	struct arch_hibernate_hdr *hdr = addr;
>> diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
>> index 8f9bc2327dc85..48f343704cb54 100644
>> --- a/arch/arm64/kernel/machine_kexec.c
>> +++ b/arch/arm64/kernel/machine_kexec.c
>> @@ -6,6 +6,7 @@
>>    * Copyright (C) Huawei Futurewei Technologies.
>>    */
>>   
>> +#include <linux/arm-rmi-cmds.h>
>>   #include <linux/interrupt.h>
>>   #include <linux/irq.h>
>>   #include <linux/kernel.h>
>> @@ -59,6 +60,16 @@ int machine_kexec_prepare(struct kimage *kimage)
>>   		return -EBUSY;
>>   	}
>>   
>> +	/*
>> +	 * We will be able to allow kdump to proceed, once we have the support
>> +	 * for handling GPF from vmcore accesses to delegated pages. Until then
>> +	 * block kexec completely.
>> +	 */
>> +	if (is_rmm_active()) {
>> +		pr_err("Can't kexec: RMM is active.\n");
>> +		return -EBUSY;
>> +	}
>> +
>>   	return 0;
>>   }
>>   
>> diff --git a/include/linux/suspend.h b/include/linux/suspend.h
>> index b02876f1ae38a..a3815027773c5 100644
>> --- a/include/linux/suspend.h
>> +++ b/include/linux/suspend.h
>> @@ -401,6 +401,7 @@ int hibernate_quiet_exec(int (*func)(void *data), void *data);
>>   int hibernate_resume_nonboot_cpu_disable(void);
>>   int arch_hibernation_header_save(void *addr, unsigned int max_size);
>>   int arch_hibernation_header_restore(void *addr);
>> +bool arch_hibernation_available(void);
>>   
>>   #else /* CONFIG_HIBERNATION */
>>   static inline void register_nosave_region(unsigned long b, unsigned long e) {}
>> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
>> index d2479c69d71a4..9d9d53828542f 100644
>> --- a/kernel/power/hibernate.c
>> +++ b/kernel/power/hibernate.c
>> @@ -106,11 +106,17 @@ bool hibernation_in_progress(void)
>>   	return !atomic_read(&hibernate_atomic);
>>   }
>>   
>> +__weak bool arch_hibernation_available(void)
>> +{
>> +	return true;
>> +}
>> +
>>   bool hibernation_available(void)
>>   {
>>   	return nohibernate == 0 &&
>>   		!security_locked_down(LOCKDOWN_HIBERNATION) &&
>> -		!secretmem_active() && !cxl_mem_active();
>> +		!secretmem_active() && !cxl_mem_active() &&
>> +		arch_hibernation_available();
>>   }
> 
> With the comments above addressed:
> 
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

Thank you!

Suzuki