Re: [PATCH v6 02/11] arm64: Detect if in a realm and set RIPAS RAM

[Gavin Shan <gshan@redhat.com>]

On 10/5/24 12:42 AM, Steven Price wrote:
> From: Suzuki K Poulose <suzuki.poulose@arm.com>
> 
> Detect that the VM is a realm guest by the presence of the RSI
> interface. This is done after PSCI has been initialised so that we can
> check the SMCCC conduit before making any RSI calls.
> 
> If in a realm then all memory needs to be marked as RIPAS RAM initially,
> the loader may or may not have done this for us. To be sure iterate over
> all RAM and mark it as such. Any failure is fatal as that implies the
> RAM regions passed to Linux are incorrect - which would mean failing
> later when attempting to access non-existent RAM.
> 
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Co-developed-by: Steven Price <steven.price@arm.com>
> Signed-off-by: Steven Price <steven.price@arm.com>
> ---
> Changes since v5:
>   * Replace BUG_ON() with a panic() call that provides a message with the
>     memory range that couldn't be set to RIPAS_RAM.
>   * Move the call to arm64_rsi_init() later so that it is after PSCI,
>     this means we can use arm_smccc_1_1_get_conduit() to check if it is
>     safe to make RSI calls.
> Changes since v4:
>   * Minor tidy ups.
> Changes since v3:
>   * Provide safe/unsafe versions for converting memory to protected,
>     using the safer version only for the early boot.
>   * Use the new psci_early_test_conduit() function to avoid calling an
>     SMC if EL3 is not present (or not configured to handle an SMC).
> Changes since v2:
>   * Use DECLARE_STATIC_KEY_FALSE rather than "extern struct
>     static_key_false".
>   * Rename set_memory_range() to rsi_set_memory_range().
>   * Downgrade some BUG()s to WARN()s and handle the condition by
>     propagating up the stack. Comment the remaining case that ends in a
>     BUG() to explain why.
>   * Rely on the return from rsi_request_version() rather than checking
>     the version the RMM claims to support.
>   * Rename the generic sounding arm64_setup_memory() to
>     arm64_rsi_setup_memory() and move the call site to setup_arch().
> ---
>   arch/arm64/include/asm/rsi.h | 66 +++++++++++++++++++++++++++++++
>   arch/arm64/kernel/Makefile   |  3 +-
>   arch/arm64/kernel/rsi.c      | 75 ++++++++++++++++++++++++++++++++++++
>   arch/arm64/kernel/setup.c    |  3 ++
>   4 files changed, 146 insertions(+), 1 deletion(-)
>   create mode 100644 arch/arm64/include/asm/rsi.h
>   create mode 100644 arch/arm64/kernel/rsi.c
> 

Two nitpicks below.

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

> diff --git a/arch/arm64/include/asm/rsi.h b/arch/arm64/include/asm/rsi.h
> new file mode 100644
> index 000000000000..e4c01796c618
> --- /dev/null
> +++ b/arch/arm64/include/asm/rsi.h
> @@ -0,0 +1,66 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (C) 2024 ARM Ltd.
> + */
> +
> +#ifndef __ASM_RSI_H_
> +#define __ASM_RSI_H_
> +
> +#include <linux/errno.h>
> +#include <linux/jump_label.h>
> +#include <asm/rsi_cmds.h>
> +
> +DECLARE_STATIC_KEY_FALSE(rsi_present);
> +
> +void __init arm64_rsi_init(void);
> +
> +static inline bool is_realm_world(void)
> +{
> +	return static_branch_unlikely(&rsi_present);
> +}
> +
> +static inline int rsi_set_memory_range(phys_addr_t start, phys_addr_t end,
> +				       enum ripas state, unsigned long flags)
> +{
> +	unsigned long ret;
> +	phys_addr_t top;
> +
> +	while (start != end) {
> +		ret = rsi_set_addr_range_state(start, end, state, flags, &top);
> +		if (WARN_ON(ret || top < start || top > end))
> +			return -EINVAL;
> +		start = top;
> +	}
> +
> +	return 0;
> +}
> +

The WARN_ON() is redundant when the caller is arm64_rsi_setup_memory(), where
system panic is invoked on any errors. So we perhaps need to drop the WARN_ON().

[...]

> +
> +static void __init arm64_rsi_setup_memory(void)
> +{
> +	u64 i;
> +	phys_addr_t start, end;
> +
> +	/*
> +	 * Iterate over the available memory ranges and convert the state to
> +	 * protected memory. We should take extra care to ensure that we DO NOT
> +	 * permit any "DESTROYED" pages to be converted to "RAM".
> +	 *
> +	 * panic() is used because if the attempt to switch the memory to
> +	 * protected has failed here, then future accesses to the memory are
> +	 * simply going to be reflected as a SEA (Synchronous External Abort)
> +	 * which we can't handle.  Bailing out early prevents the guest limping
> +	 * on and dying later.
> +	 */
> +	for_each_mem_range(i, &start, &end) {
> +		if (rsi_set_memory_range_protected_safe(start, end))
> +			panic("Failed to set memory range to protected: %pa-%pa",
> +			      &start, &end);
> +	}
> +}
> +

{} is needed since the panic statement spans multiple lines.

Thanks,
Gavin