Re: [PATCH v4 03/15] arm64: Detect if in a realm and set RIPAS RAM

Gavin Shan
2024-07-29T23:37:35Z

On 7/1/24 7:54 PM, 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.
>
> 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 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 | 64 +++++++++++++++++++++++++
> arch/arm64/include/asm/rsi_cmds.h | 22 +++++++++
> arch/arm64/kernel/Makefile | 3 +-
> arch/arm64/kernel/rsi.c | 77 +++++++++++++++++++++++++++++++
> arch/arm64/kernel/setup.c | 8 ++++
> 5 files changed, 173 insertions(+), 1 deletion(-)
> create mode 100644 arch/arm64/include/asm/rsi.h
> create mode 100644 arch/arm64/kernel/rsi.c
>
> diff --git a/arch/arm64/include/asm/rsi.h b/arch/arm64/include/asm/rsi.h
> new file mode 100644
> index 000000000000..29fdc194d27b
> --- /dev/null
> +++ b/arch/arm64/include/asm/rsi.h
> @@ -0,0 +1,64 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (C) 2024 ARM Ltd.
> + */
> +
> +#ifndef __ASM_RSI_H_
> +#define __ASM_RSI_H_
> +
> +#include <linux/jump_label.h>
> +#include <asm/rsi_cmds.h>
> +
> +DECLARE_STATIC_KEY_FALSE(rsi_present);
> +
> +void __init arm64_rsi_init(void);
> +void __init arm64_rsi_setup_memory(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;
> +}
> +

@flags has been defined as int instead of unsigned long, which is inconsistent
to TF-RMM's definitions since it has type of 'unsigned long'.

> +/*
> + * Convert the specified range to RAM. Do not use this if you rely on the
> + * contents of a page that may already be in RAM state.
> + */
> +static inline int rsi_set_memory_range_protected(phys_addr_t start,
> + phys_addr_t end)
> +{
> + return rsi_set_memory_range(start, end, RSI_RIPAS_RAM,
> + RSI_CHANGE_DESTROYED);
> +}
> +
> +/*
> + * Convert the specified range to RAM. Do not convert any pages that may have
> + * been DESTROYED, without our permission.
> + */
> +static inline int rsi_set_memory_range_protected_safe(phys_addr_t start,
> + phys_addr_t end)
> +{
> + return rsi_set_memory_range(start, end, RSI_RIPAS_RAM,
> + RSI_NO_CHANGE_DESTROYED);
> +}
> +
> +static inline int rsi_set_memory_range_shared(phys_addr_t start,
> + phys_addr_t end)
> +{
> + return rsi_set_memory_range(start, end, RSI_RIPAS_EMPTY, 0);
> +}
> +#endif

s/0/RSI_NO_CHANGE_DESTROYED
s/#endif/#endif /* __ASM_RSI_H_ */

> diff --git a/arch/arm64/include/asm/rsi_cmds.h b/arch/arm64/include/asm/rsi_cmds.h
> index 89e907f3af0c..acb557dd4b88 100644
> --- a/arch/arm64/include/asm/rsi_cmds.h
> +++ b/arch/arm64/include/asm/rsi_cmds.h
> @@ -10,6 +10,11 @@
>
> #include <asm/rsi_smc.h>
>
> +enum ripas {
> + RSI_RIPAS_EMPTY,
> + RSI_RIPAS_RAM,
> +};
> +
> static inline unsigned long rsi_request_version(unsigned long req,
> unsigned long *out_lower,
> unsigned long *out_higher)
> @@ -35,4 +40,21 @@ static inline unsigned long rsi_get_realm_config(struct realm_config *cfg)
> return res.a0;
> }
>
> +static inline unsigned long rsi_set_addr_range_state(phys_addr_t start,
> + phys_addr_t end,
> + enum ripas state,
> + unsigned long flags,
> + phys_addr_t *top)
> +{
> + struct arm_smccc_res res;
> +
> + arm_smccc_smc(SMC_RSI_IPA_STATE_SET, start, end, state,
> + flags, 0, 0, 0, &res);
> +
> + if (top)
> + *top = res.a1;
> +
> + return res.a0;
> +}
> +
> #endif
> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
> index 763824963ed1..a483b916ed11 100644
> --- a/arch/arm64/kernel/Makefile
> +++ b/arch/arm64/kernel/Makefile
> @@ -33,7 +33,8 @@ obj-y := debug-monitors.o entry.o irq.o fpsimd.o \
> return_address.o cpuinfo.o cpu_errata.o \
> cpufeature.o alternative.o cacheinfo.o \
> smp.o smp_spin_table.o topology.o smccc-call.o \
> - syscall.o proton-pack.o idle.o patching.o pi/
> + syscall.o proton-pack.o idle.o patching.o pi/ \
> + rsi.o
>
> obj-$(CONFIG_COMPAT) += sys32.o signal32.o \
> sys_compat.o
> diff --git a/arch/arm64/kernel/rsi.c b/arch/arm64/kernel/rsi.c
> new file mode 100644
> index 000000000000..f01bff9dab04
> --- /dev/null
> +++ b/arch/arm64/kernel/rsi.c
> @@ -0,0 +1,77 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2023 ARM Ltd.
> + */
> +
> +#include <linux/jump_label.h>
> +#include <linux/memblock.h>
> +#include <linux/psci.h>
> +#include <asm/rsi.h>
> +
> +DEFINE_STATIC_KEY_FALSE_RO(rsi_present);
> +EXPORT_SYMBOL(rsi_present);
> +
> +static bool rsi_version_matches(void)
> +{
> + unsigned long ver_lower, ver_higher;
> + unsigned long ret = rsi_request_version(RSI_ABI_VERSION,
> + &ver_lower,
> + &ver_higher);
> +
> + if (ret == SMCCC_RET_NOT_SUPPORTED)
> + return false;
> +
> + if (ret != RSI_SUCCESS) {
> + pr_err("RME: RMM doesn't support RSI version %u.%u. Supported range: %lu.%lu-%lu.%lu\n",
> + RSI_ABI_VERSION_MAJOR, RSI_ABI_VERSION_MINOR,
> + RSI_ABI_VERSION_GET_MAJOR(ver_lower),
> + RSI_ABI_VERSION_GET_MINOR(ver_lower),
> + RSI_ABI_VERSION_GET_MAJOR(ver_higher),
> + RSI_ABI_VERSION_GET_MINOR(ver_higher));
> + return false;
> + }
> +
> + pr_info("RME: Using RSI version %lu.%lu\n",
> + RSI_ABI_VERSION_GET_MAJOR(ver_lower),
> + RSI_ABI_VERSION_GET_MINOR(ver_lower));
> +
> + return true;
> +}
> +
> +void __init arm64_rsi_setup_memory(void)
> +{
> + u64 i;
> + phys_addr_t start, end;
> +
> + if (!is_realm_world())
> + return;
> +
> + /*
> + * Iterate over the available memory ranges and convert the state to
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
blocks and convert them to

> + * protected memory. We should take extra care to ensure that we DO NOT
> + * permit any "DESTROYED" pages to be converted to "RAM".
> + *
> + * BUG_ON 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 fault which we can't handle.
> + * Bailing out early prevents the guest limping on and dieing later.
> + */
> + for_each_mem_range(i, &start, &end) {
> + BUG_ON(rsi_set_memory_range_protected_safe(start, end));
> + }
> +}
> +

If I'm understanding the code completely, this changes the memory state from
RIPAS_EMPTY to RIPAS_RAM so that the following page faults can be routed to
host properly. Otherwise, a SEA is injected to the realm according to
tf-rmm/runtime/core/exit.c::handle_data_abort(). The comments can be more
explicit to replace "fault" with "SEA (Synchronous External Abort)".

Besides, this forces a guest exit with reason RMI_EXIT_RIPAS_CHANGE which is
handled by the host, where RMI_RTT_SET_RIPAS is triggered to convert the memory
state from RIPAS_EMPTY to RIPAS_RAM. The question is why the conversion can't
be done by VMM (QEMU)?

> +void __init arm64_rsi_init(void)
> +{
> + /*
> + * If PSCI isn't using SMC, RMM isn't present. Don't try to execute an
> + * SMC as it could be UNDEFINED.
> + */
> + if (!psci_early_test_conduit(SMCCC_CONDUIT_SMC))
> + return;
> + if (!rsi_version_matches())
> + return;
> +
> + static_branch_enable(&rsi_present);
> +}
> +
> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
> index a096e2451044..143f87615af0 100644
> --- a/arch/arm64/kernel/setup.c
> +++ b/arch/arm64/kernel/setup.c
> @@ -43,6 +43,7 @@
> #include <asm/cpu_ops.h>
> #include <asm/kasan.h>
> #include <asm/numa.h>
> +#include <asm/rsi.h>
> #include <asm/scs.h>
> #include <asm/sections.h>
> #include <asm/setup.h>
> @@ -293,6 +294,11 @@ void __init __no_sanitize_address setup_arch(char **cmdline_p)
> * cpufeature code and early parameters.
> */
> jump_label_init();
> + /*
> + * Init RSI before early param so that "earlycon" console uses the
> + * shared alias when in a realm
> + */
> + arm64_rsi_init();
> parse_early_param();
>
> dynamic_scs_init();
> @@ -328,6 +334,8 @@ void __init __no_sanitize_address setup_arch(char **cmdline_p)
>
> arm64_memblock_init();
>
> + arm64_rsi_setup_memory();
> +
> paging_init();
>
> acpi_table_upgrade();

Thanks,
Gavin