Hi Raghu,

Thanks for sharing this work.

Few thoughts...

1/ I guess it requires an additional change in project/reference to eventually enable the feature for a platform (enable_vhe=1 in the gn build flow)?

Sorry if my questions below sound obvious, I may miss bits of the VHE architecture.

2/ The changes are effectively toggling HCR_EL2.E2H=1. Currently when Hafnium ERETs resuming a SP, this happens with the secure EL1&0 translation regime. Though what's the next step forward? Does this require a host OS in secure world? (like linux does when booting under a Hypervisor with VHE enabled?) Would this be a VHE-enabled TOS?

3/ Is the later goal to enable the secure EL2&0 translation regime?

4/ Is there anything to do with HCR_EL2.TGE?

Regards, Olivier.

________________________________________ From: Hafnium hafnium-bounces@lists.trustedfirmware.org on behalf of Raghu Krishnamurthy via Hafnium hafnium@lists.trustedfirmware.org Sent: 15 December 2020 04:57 To: hafnium@lists.trustedfirmware.org Subject: [Hafnium] VHE support

Hi All,

I have a series of patches pushed to Gerrit at https://review.trustedfirmware.org/c/hafnium/hafnium/+/7599 with topic "vhe_enable". The goal of this patch series is to enable VM's in both secure and normal world to run with VHE enabled(hcr_el2.e2h=1), without breaking any existing functionality. This is expected to be the first step in the long term goal of enabling S-EL0 partitions(and optionally EL0 partitions), that require VHE support, per the FF-A 1.0 Spec. I'd appreciate feedback on the patches and approach taken to nominally enabling VHE. Note that the FF-A 1.0 spec(AFAIK) does not expect VHE support in the normal world but this patch series enables it anyway due to the wealth of available tests in the hafnium test suite to help with providing confidence in the implementation.

The patch series has been tested as follows:

Hafnium tests using QEMU(prebuilt in the hafnium repo) - Without VHE, since the prebuilt QEMU does not support VHE.

Hafnium tests using QEMU(5.2-RC4, built from source) - With and without VHE, this version of QEMU supports VHE.

Hafnium tests using FVP 11.12.28 - With and Without VHE.

TFTF tests for secure hafnium using FVP 11.12.28 - With and without VHE.

Thanks

Raghu

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