linux-kernel - Re: [PATCH v9 17/43] arm64: RME: Handle RMI_EXIT_RIPAS

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Message-ID: <5eef96b4-2a33-4d52-a68a-323709beee5b@redhat.com>
Date: Wed, 2 Jul 2025 10:44:12 +1000
From: Gavin Shan <gshan@...hat.com>
To: Steven Price <steven.price@....com>, kvm@...r.kernel.org,
 kvmarm@...ts.linux.dev
Cc: Catalin Marinas <catalin.marinas@....com>, Marc Zyngier <maz@...nel.org>,
 Will Deacon <will@...nel.org>, James Morse <james.morse@....com>,
 Oliver Upton <oliver.upton@...ux.dev>,
 Suzuki K Poulose <suzuki.poulose@....com>, Zenghui Yu
 <yuzenghui@...wei.com>, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, Joey Gouly <joey.gouly@....com>,
 Alexandru Elisei <alexandru.elisei@....com>,
 Christoffer Dall <christoffer.dall@....com>, Fuad Tabba <tabba@...gle.com>,
 linux-coco@...ts.linux.dev,
 Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>,
 Shanker Donthineni <sdonthineni@...dia.com>, Alper Gun
 <alpergun@...gle.com>, "Aneesh Kumar K . V" <aneesh.kumar@...nel.org>,
 Emi Kisanuki <fj0570is@...itsu.com>
Subject: Re: [PATCH v9 17/43] arm64: RME: Handle RMI_EXIT_RIPAS_CHANGE

On 6/11/25 8:48 PM, Steven Price wrote:
> The guest can request that a region of it's protected address space is
> switched between RIPAS_RAM and RIPAS_EMPTY (and back) using
> RSI_IPA_STATE_SET. This causes a guest exit with the
> RMI_EXIT_RIPAS_CHANGE code. We treat this as a request to convert a
> protected region to unprotected (or back), exiting to the VMM to make
> the necessary changes to the guest_memfd and memslot mappings. On the
> next entry the RIPAS changes are committed by making RMI_RTT_SET_RIPAS
> calls.
> 
> The VMM may wish to reject the RIPAS change requested by the guest. For
> now it can only do with by no longer scheduling the VCPU as we don't
> currently have a usecase for returning that rejection to the guest, but
> by postponing the RMI_RTT_SET_RIPAS changes to entry we leave the door
> open for adding a new ioctl in the future for this purpose.
> 
> Signed-off-by: Steven Price <steven.price@....com>
> ---
> Changes since v8:
>   * Make use of ripas_change() from a previous patch to implement
>     realm_set_ipa_state().
>   * Update exit.ripas_base after a RIPAS change so that, if instead of
>     entering the guest we exit to user space, we don't attempt to repeat
>     the RIPAS change (triggering an error from the RMM).
> Changes since v7:
>   * Rework the loop in realm_set_ipa_state() to make it clear when the
>     'next' output value of rmi_rtt_set_ripas() is used.
> New patch for v7: The code was previously split awkwardly between two
> other patches.
> ---
>   arch/arm64/kvm/rme.c | 46 ++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 46 insertions(+)
> 

Reviewed-by: Gavin Shan <gshan@...hat.com>