From: Kameron Carr <[email protected]> Sent: Thursday, June 25,
2026 10:35 AM
> To: [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]
> Cc: [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]; linux-
> [email protected]; [email protected]; linux-
> [email protected]; [email protected]; [email protected]
> Subject: [PATCH v2 3/6] arm64: hyperv: Add per-CPU RSI host call
> infrastructure for CCA
> Realms
>
> Arm CCA Realms cannot issue Hyper-V hypercalls via HVC; the guest must
> route them through the RSI_HOST_CALL interface, which takes the IPA of a
> per-CPU rsi_host_call structure as its argument.
>
> Add hv_hostcall_array as a per-CPU struct array and allocate it during
> hyperv_init(). The allocation is gated on is_realm_world() so non-Realm
> arm64 Hyper-V guests pay no memory cost.
>
> Signed-off-by: Kameron Carr <[email protected]>
> ---
> arch/arm64/hyperv/mshyperv.c | 32 ++++++++++++++++++++++++++++++-
> arch/arm64/include/asm/mshyperv.h | 4 ++++
> 2 files changed, 35 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
> index 4fdc26ade1d74..7d536d7fb557e 100644
> --- a/arch/arm64/hyperv/mshyperv.c
> +++ b/arch/arm64/hyperv/mshyperv.c
> @@ -15,10 +15,15 @@
> #include <linux/errno.h>
> #include <linux/version.h>
> #include <linux/cpuhotplug.h>
> +#include <linux/slab.h>
> #include <asm/mshyperv.h>
> +#include <asm/rsi.h>
>
> static bool hyperv_initialized;
>
> +struct rsi_host_call *hv_hostcall_array;
> +EXPORT_SYMBOL_GPL(hv_hostcall_array);
> +
> int hv_get_hypervisor_version(union hv_hypervisor_version_info *info)
> {
> hv_get_vpreg_128(HV_REGISTER_HYPERVISOR_VERSION,
> @@ -60,6 +65,12 @@ static bool __init hyperv_detect_via_acpi(void)
>
> #endif
>
> +static void hv_hostcall_free(void)
> +{
> + kfree(hv_hostcall_array);
> + hv_hostcall_array = NULL;
> +}
> +
> static bool __init hyperv_detect_via_smccc(void)
> {
> uuid_t hyperv_uuid = UUID_INIT(
> @@ -85,6 +96,20 @@ static int __init hyperv_init(void)
> if (!hyperv_detect_via_acpi() && !hyperv_detect_via_smccc())
> return 0;
>
> + /*
> + * The RSI host-call buffers are only ever used when
> + * is_realm_world() is true. Skip the allocation on non-Realm
> + * guests. A single contiguous array of nr_cpu_ids entries is
> + * allocated; each CPU indexes into it by its processor ID.
> + */
> + if (is_realm_world()) {
> + hv_hostcall_array = kcalloc(nr_cpu_ids,
> + sizeof(struct rsi_host_call),
> + GFP_KERNEL);
> + if (!hv_hostcall_array)
> + return -ENOMEM;
> + }
> +
> /* Setup the guest ID */
> guest_id = hv_generate_guest_id(LINUX_VERSION_CODE);
> hv_set_vpreg(HV_REGISTER_GUEST_OS_ID, guest_id);
> @@ -106,12 +131,13 @@ static int __init hyperv_init(void)
>
> ret = hv_common_init();
> if (ret)
> - return ret;
> + goto free_hostcall_mem;
>
> ret = cpuhp_setup_state(CPUHP_AP_HYPERV_ONLINE,
> "arm64/hyperv_init:online",
> hv_common_cpu_init, hv_common_cpu_die);
> if (ret < 0) {
> hv_common_free();
> + hv_hostcall_free();
> return ret;
Let me suggest a small additional simplification. For this error
path, call hv_common_free() as you have now, but then do
"goto free_hostcall_mem". At the free_hostcall_mem label, do
kfree(hv_hostcall_array);
hv_hostcall_array = NULL;
directly inline, and eliminate the hv_hostcall_free() helper
function. Saves about 5 lines of code overall and I think is a
bit simpler.
> }
>
> @@ -125,6 +151,10 @@ static int __init hyperv_init(void)
>
> hyperv_initialized = true;
> return 0;
> +
> +free_hostcall_mem:
> + hv_hostcall_free();
> + return ret;
> }
>
> early_initcall(hyperv_init);
> diff --git a/arch/arm64/include/asm/mshyperv.h
> b/arch/arm64/include/asm/mshyperv.h
> index b721d3134ab66..c207a3f79b99b 100644
> --- a/arch/arm64/include/asm/mshyperv.h
> +++ b/arch/arm64/include/asm/mshyperv.h
> @@ -63,4 +63,8 @@ static inline u64 hv_get_non_nested_msr(unsigned int reg)
>
> #include <asm-generic/mshyperv.h>
>
> +/* Per-CPU-indexed RSI host call structures for CCA Realms */
> +struct rsi_host_call;
> +extern struct rsi_host_call *hv_hostcall_array;
> +
The intent is that the #include of asm-generic/mshyperv.h should be
last in the arch-specific version of mshyperv.h. If there's a need to go
after the #include, that's a red flag to check if some restructuring of
the definitions would be appropriate.
Unless I'm missing something, I think these new definitions can go
above the #include.
Michael
> #endif
> --
> 2.45.4
>
