From: Catalin Marinas <catalin.marinas@arm•com>
To: Suzuki K Poulose <suzuki.poulose@arm•com>
Cc: linux-arm-kernel@lists•infradead.org,
linux-kernel@vger•kernel.org, will@kernel•org, ardb@kernel•org,
lpieralisi@kernel•org, mark.rutland@arm•com,
steven.price@arm•com, aneesh.kumar@kernel•org,
sudeep.holla@arm•com, robh@kernel•org, maz@kernel•org
Subject: Re: [RFC PATCH v2 0/4] arm64: realm: Support for probing RSI earlier
Date: Thu, 28 May 2026 17:06:39 +0100 [thread overview]
Message-ID: <ahhoD3HbKMo_vP8K@arm.com> (raw)
In-Reply-To: <20260505155742.623287-1-suzuki.poulose@arm.com>
Hi Suzuki,
On Tue, May 05, 2026 at 04:57:38PM +0100, Suzuki K Poulose wrote:
> This is an updated series, addressing the review comments from AI agent on
> the version 1 [0] of the series, (some of which were documented as short comings).
> See below for the changes.
>
> The Realm Guest linux support is broken without rodata=full (fortunately default
> for arm64), as we detect the RSI support after we have created the Linear map
> with Block/Contiguous mappings. If the boot CPU doesn't support BBML2_NOABORT
> (there are CPUs out there with FEAT_RME and no - useable - BBML2_NOABORT)
> we are then not able to split the page tables down to PTE level if the system
> as such doesn't support BBML2.
>
> See the following link for the discussion.
>
> https://lore.kernel.org/all/20260330161705.3349825-2-ryan.roberts@arm.com/
>
> The available options are :
> 1. Start with PTE level mappings at paging_init() and then "FOLD" the page tables
> to Block/Cont mappings after we have the full picture available. Looking at the
> future (with BBML3), this might mean "additional work" for most of the systems
> at boot. But not bad as splitting them ?
> 2. Hold the secondary CPUs in busy loop with MMU disabled and split the mappings
> by the boot CPU with MMU off (if Boot CPU can't support BBML2). This is tricky
> with the page allocations required to add the page-tables.
> 3. Move the detection of Realm support earlier to make a better decision for
> paging_init(), with an added bonus of earlycon support for Realms without
> the user having to work out the "top bit" for the Realm.
>
> This series is an attempt to implement (3) (without the earlycon support). We try
> to probe the PSCI conduit early from the DT/ACPI. DT is not flattened at this time.
Looking at the patches, I'm no longer sure it's worth justifying the
complexity. Trying to recall the previous thread - does it only matter
if BBML2_NOABORT is not supported and the kernel boots with rodata=off?
I guess we can ignore big.LITTLE configurations for now since the
deployment of CCA doesn't target mobile yet.
Could we instead add a more informative message in arm64_rsi_init() if
!force_pte_mappings() && !cpu_supports_bbml2_noabort() (before
is_realm_world() becomes true)? Well, it may not print anything if the
early console is not set up yet.
--
Catalin
next prev parent reply other threads:[~2026-05-28 16:06 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-29 10:35 [RFC PATCH 0/4] arm64: realm: Support for probing RSI earlier Suzuki K Poulose
2026-04-29 10:35 ` [RFC PATCH 1/4] arm64: acpi: Refactor FADT table verification Suzuki K Poulose
2026-04-29 10:35 ` [RFC PATCH 2/4] psci: Add support for Early detection and init Suzuki K Poulose
2026-04-29 10:35 ` [RFC PATCH 3/4] arm64: psci: Move detection and SMCCC probe earlier Suzuki K Poulose
2026-04-29 10:35 ` [RFC PATCH 4/4] arm64: realm: Move RSI detection earlier Suzuki K Poulose
2026-05-05 15:57 ` [RFC PATCH v2 0/4] arm64: realm: Support for probing RSI earlier Suzuki K Poulose
2026-05-05 15:57 ` [RFC PATCH v2 1/4] arm64: acpi: Refactor FADT table verification Suzuki K Poulose
2026-05-05 15:57 ` [RFC PATCH v2 2/4] psci: Add support for Early detection and init Suzuki K Poulose
2026-05-05 15:57 ` [RFC PATCH v2 3/4] arm64: psci: Move detection and SMCCC probe earlier Suzuki K Poulose
2026-05-05 15:57 ` [RFC PATCH v2 4/4] arm64: realm: Move RSI detection earlier Suzuki K Poulose
2026-05-28 16:06 ` Catalin Marinas [this message]
2026-05-29 12:27 ` [RFC PATCH v2 0/4] arm64: realm: Support for probing RSI earlier Suzuki K Poulose
2026-05-08 8:09 ` [RFC PATCH " Lorenzo Pieralisi
2026-05-08 8:28 ` Suzuki K Poulose
2026-05-08 11:05 ` Lorenzo Pieralisi
2026-05-13 10:17 ` Suzuki K Poulose
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