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Re: [PATCH v8 10/13] xen/arm: Resume memory management on Xen resume
- To: Mykola Kvach <xakep.amatop@xxxxxxxxx>
- From: Luca Fancellu <Luca.Fancellu@xxxxxxx>
- Date: Fri, 8 May 2026 13:26:54 +0000
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Mykola Kvach <mykola_kvach@xxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Delivery-date: Fri, 08 May 2026 13:28:25 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-index: AQHc1lUPIk7A8CPopkGFdHGIM/WlP7X/oqWAgASNN4A=
- Thread-topic: [PATCH v8 10/13] xen/arm: Resume memory management on Xen resume
Hi Mykola,
>>> xen/arch/arm/arm64/head.S | 24 ++++++++++++++++++++++++
>>> 1 file changed, 24 insertions(+)
>>>
>>> diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
>>> index 72c7b24498..596e960152 100644
>>> --- a/xen/arch/arm/arm64/head.S
>>> +++ b/xen/arch/arm/arm64/head.S
>>> @@ -561,6 +561,30 @@ END(efi_xen_start)
>>>
>>> #endif /* CONFIG_ARM_EFI */
>>>
>>> +#ifdef CONFIG_SYSTEM_SUSPEND
>>> +
>>> +FUNC(hyp_resume)
>>
>> I think we should mask all exceptions here:
>> msr DAIFSet, 0xf
>>
>> until we resume correctly the status (VBAR_EL2, etc).
>
> This was discussed in an earlier version:
>
> https://patchew.org/Xen/cover.1741164138.git.xakep.amatop@xxxxxxxxx/2ef15cb605f987eb087c5496d123c47c01cc0ae7.1741164138.git.xakep.amatop@xxxxxxxxx/#CAGeoDV97no7mXSKd7auFu5E85wSXAHKWvqGW2=-VEAbkrTyU8Q@xxxxxxxxxxxxxx
>
> For SYSTEM_SUSPEND, PSCI ties the call semantics to CPU_SUSPEND. In
> particular, section 5.20.2 says that the caller must observe all the rules
> described for CPU_SUSPEND, and section 6.4 explicitly says that the initial
> state rules also apply to SYSTEM_SUSPEND.
>
> For the return Exception level on AArch64, section 6.4.3.3 requires
> SPSR_ELx.{D,A,I,F} to be set to {1, 1, 1, 1}. Therefore Xen expects to enter
> this resume path with DAIF already masked by PSCI-compliant firmware.
>
> I agree this assumption is not obvious from the code, so I will add a comment
> at the resume entry point to document that this path relies on the PSCI
> initial
> core configuration requirements.
Yes please, something along the line of
/*
* PSCI SYSTEM_SUSPEND follows CPU_SUSPEND initial-state rules.
* On AArch64, firmware must return with SPSR_ELx.DAIF set, so
* PSTATE.DAIF is already masked on entry here.
*/
Cheers,
Luca
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