[PATCH v3 20/23] kvm: arm64: Intercept host's CPU_SUSPEND PSCI SMCs

David Brazdil
2020-11-26T15:55:32Z

Add a handler of CPU_SUSPEND host PSCI SMCs. The SMC can either enter
a sleep state indistinguishable from a WFI or a deeper sleep state that
behaves like a CPU_OFF+CPU_ON except that the core is still considered
online when asleep.

The handler saves r0,pc of the host and makes the same call to EL3 with
the hyp CPU entry point. It either returns back to the handler and then
back to the host, or wakes up into the entry point and initializes EL2
state before dropping back to EL1.

A core can only suspend itself but other cores can concurrently invoke
CPU_ON with this core as target. To avoid racing them for the same
boot args struct, CPU_SUSPEND uses a different struct instance and entry
point. Each entry point selects the corresponding struct to restore host
boot args from. This avoids the need for locking in CPU_SUSPEND.

Signed-off-by: David Brazdil <dbrazdil@google.com>
---
arch/arm64/kvm/hyp/nvhe/hyp-init.S | 9 +++++
arch/arm64/kvm/hyp/nvhe/psci-relay.c | 50 +++++++++++++++++++++++++---
2 files changed, 54 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-init.S b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
index ea71f653af55..fbb195851fb9 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-init.S
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
@@ -162,7 +162,15 @@ alternative_else_nop_endif
ret
SYM_CODE_END(___kvm_hyp_init)

+SYM_CODE_START(__kvm_hyp_cpu_suspend_entry)
+ mov x28, #0 // is_cpu_on = false
+ b __kvm_hyp_cpu_common_entry
+SYM_CODE_END(__kvm_hyp_cpu_suspend_entry)
+
SYM_CODE_START(__kvm_hyp_cpu_on_entry)
+ mov x28, #1 // is_cpu_on = true
+
+SYM_INNER_LABEL(__kvm_hyp_cpu_common_entry, SYM_L_LOCAL)
msr SPsel, #1 // We want to use SP_EL{1,2}

/* Check that the core was booted in EL2. */
@@ -188,6 +196,7 @@ SYM_CODE_START(__kvm_hyp_cpu_on_entry)
kimg_hyp_va x1, x2

/* Leave idmap. */
+ mov x0, x28
br x1
SYM_CODE_END(__kvm_hyp_cpu_on_entry)

diff --git a/arch/arm64/kvm/hyp/nvhe/psci-relay.c b/arch/arm64/kvm/hyp/nvhe/psci-relay.c
index 39e507672e6e..592c11e9851c 100644
--- a/arch/arm64/kvm/hyp/nvhe/psci-relay.c
+++ b/arch/arm64/kvm/hyp/nvhe/psci-relay.c
@@ -17,6 +17,7 @@
#include <nvhe/trap_handler.h>

extern char __kvm_hyp_cpu_on_entry[];
+extern char __kvm_hyp_cpu_suspend_entry[];

void __noreturn __host_enter(struct kvm_cpu_context *host_ctxt);

@@ -39,6 +40,7 @@ struct cpu_boot_args {

static DEFINE_PER_CPU(atomic_t, cpu_on_lock) = ATOMIC_INIT(0);
static DEFINE_PER_CPU(struct cpu_boot_args, cpu_on_args);
+static DEFINE_PER_CPU(struct cpu_boot_args, cpu_suspend_args);

static u64 get_psci_func_id(struct kvm_cpu_context *host_ctxt)
{
@@ -112,6 +114,34 @@ static unsigned int find_cpu_id(u64 mpidr)
return INVALID_CPU_ID;
}

+static int psci_cpu_suspend(u64 func_id, struct kvm_cpu_context *host_ctxt)
+{
+ DECLARE_REG(u64, power_state, host_ctxt, 1);
+ DECLARE_REG(unsigned long, pc, host_ctxt, 2);
+ DECLARE_REG(unsigned long, r0, host_ctxt, 3);
+
+ struct cpu_boot_args *boot_args;
+ struct kvm_nvhe_init_params *init_params;
+
+ boot_args = this_cpu_ptr(hyp_symbol_addr(cpu_suspend_args));
+ init_params = this_cpu_ptr(hyp_symbol_addr(kvm_init_params));
+
+ /*
+ * No need to acquire a lock before writing to boot_args because a core
+ * can only suspend itself and the racy CPU_ON uses a separate struct.
+ */
+
+ *boot_args = (struct cpu_boot_args){ .pc = pc, .r0 = r0 };
+
+ /*
+ * Will either return if shallow sleep state, or wake up into the entry
+ * point if it is a deep sleep state.
+ */
+ return psci_call(func_id, power_state,
+ __hyp_pa(hyp_symbol_addr(__kvm_hyp_cpu_suspend_entry)),
+ __hyp_pa(init_params));
+}
+
static __always_inline bool try_acquire_cpu_on_lock(atomic_t *l) {
return atomic_cmpxchg_acquire(l, CPU_UNLOCKED, CPU_LOCKED) == CPU_UNLOCKED;
}
@@ -165,27 +195,35 @@ static int psci_cpu_on(u64 func_id, struct kvm_cpu_context *host_ctxt)
return ret;
}

-asmlinkage void __noreturn __kvm_hyp_psci_cpu_entry(void)
+asmlinkage void __noreturn __kvm_hyp_psci_cpu_entry(bool is_cpu_on)
{
atomic_t *lock;
struct cpu_boot_args *boot_args;
struct kvm_cpu_context *host_ctxt;

- lock = this_cpu_ptr(hyp_symbol_addr(cpu_on_lock));
- boot_args = this_cpu_ptr(hyp_symbol_addr(cpu_on_args));
+ if (is_cpu_on)
+ boot_args = this_cpu_ptr(hyp_symbol_addr(cpu_on_args));
+ else
+ boot_args = this_cpu_ptr(hyp_symbol_addr(cpu_suspend_args));
+
host_ctxt = &this_cpu_ptr(hyp_symbol_addr(kvm_host_data))->host_ctxt;

cpu_reg(host_ctxt, 0) = boot_args->r0;
write_sysreg_el2(boot_args->pc, SYS_ELR);

- release_cpu_on_lock(lock);
+ if (is_cpu_on) {
+ lock = this_cpu_ptr(hyp_symbol_addr(cpu_on_lock));
+ release_cpu_on_lock(lock);
+ }

__host_enter(host_ctxt);
}

static unsigned long psci_0_1_handler(u64 func_id, struct kvm_cpu_context *host_ctxt)
{
- if (func_id == kvm_host_psci_function_id[PSCI_FN_CPU_OFF])
+ if (func_id == kvm_host_psci_function_id[PSCI_FN_CPU_SUSPEND])
+ return psci_cpu_suspend(func_id, host_ctxt);
+ else if (func_id == kvm_host_psci_function_id[PSCI_FN_CPU_OFF])
return psci_forward(host_ctxt);
else if (func_id == kvm_host_psci_function_id[PSCI_FN_CPU_ON])
return psci_cpu_on(func_id, host_ctxt);
@@ -209,6 +247,8 @@ static unsigned long psci_0_2_handler(u64 func_id, struct kvm_cpu_context *host_
case PSCI_0_2_FN_SYSTEM_RESET:
psci_forward_noreturn(host_ctxt);
unreachable();
+ case PSCI_0_2_FN64_CPU_SUSPEND:
+ return psci_cpu_suspend(func_id, host_ctxt);
case PSCI_0_2_FN64_CPU_ON:
return psci_cpu_on(func_id, host_ctxt);
default:
--
2.29.2.454.gaff20da3a2-goog