linux-kernel - Re: [PATCH v8 33/43] arm64: RME: Hide KVM_CAP_READONLY

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Message-ID: <fd1936c7-cc82-4dd9-9bc0-2b25a3bbbb91@redhat.com>
Date: Thu, 1 May 2025 13:01:06 +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>
Subject: Re: [PATCH v8 33/43] arm64: RME: Hide KVM_CAP_READONLY_MEM for realm
 guests

On 4/16/25 11:41 PM, Steven Price wrote:
> For protected memory read only isn't supported by the RMM. While it may
> be possible to support read only for unprotected memory, this isn't
> supported at the present time.
> 
> Note that this does mean that ROM (or flash) data cannot be emulated
> correctly by the VMM as the stage 2 mappings are either always
> read/write or are trapped as MMIO (so don't support operations where the
> syndrome information doesn't allow emulation, e.g. load/store pair).
> 
> This restriction can be lifted in the future by allowing the stage 2
> mappings to be made read only.
> 
> Signed-off-by: Steven Price <steven.price@....com>
> ---
> Changes since v7:
>   * Updated commit message to spell out the impact on ROM/flash
>     emulation.
> ---
>   arch/arm64/kvm/arm.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 

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