Re: [PATCH v3 19/23] kvm: arm64: Intercept host's CPU_ON SMCs

Sudeep Holla
2020-11-27T17:47:51Z

On Thu, Nov 26, 2020 at 03:54:17PM +0000, David Brazdil wrote:
> Add a handler of the CPU_ON PSCI call from host. When invoked, it looks
> up the logical CPU ID corresponding to the provided MPIDR and populates
> the state struct of the target CPU with the provided x0, pc. It then
> calls CPU_ON itself, with an entry point in hyp that initializes EL2
> state before returning ERET to the provided PC in EL1.
>
> There is a simple atomic lock around the boot args struct. If it is
> already locked, CPU_ON will return PENDING_ON error code.
>
> Signed-off-by: David Brazdil <dbrazdil@google.com>
> ---
> arch/arm64/kvm/hyp/nvhe/hyp-init.S | 30 ++++++++
> arch/arm64/kvm/hyp/nvhe/psci-relay.c | 109 +++++++++++++++++++++++++++
> 2 files changed, 139 insertions(+)
>
> diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-init.S b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
> index 98ce40e17b42..ea71f653af55 100644
> --- a/arch/arm64/kvm/hyp/nvhe/hyp-init.S
> +++ b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
> @@ -9,6 +9,7 @@
>
> #include <asm/alternative.h>
> #include <asm/assembler.h>
> +#include <asm/el2_setup.h>
> #include <asm/kvm_arm.h>
> #include <asm/kvm_asm.h>
> #include <asm/kvm_mmu.h>
> @@ -161,6 +162,35 @@ alternative_else_nop_endif
> ret
> SYM_CODE_END(___kvm_hyp_init)
>
> +SYM_CODE_START(__kvm_hyp_cpu_on_entry)
> + msr SPsel, #1 // We want to use SP_EL{1,2}
> +
> + /* Check that the core was booted in EL2. */
> + mrs x1, CurrentEL
> + cmp x1, #CurrentEL_EL2
> + b.eq 2f
> +
> + /* The core booted in EL1. KVM cannot be initialized on it. */
> +1: wfe
> + wfi
> + b 1b
> +
> + /* Initialize EL2 CPU state to sane values. */
> +2: mov x29, x0
> + init_el2_state nvhe
> + mov x0, x29
> +
> + /* Enable MMU, set vectors and stack. */
> + bl ___kvm_hyp_init
> +
> + /* Load address of the C handler. */
> + ldr x1, =__kvm_hyp_psci_cpu_entry
> + kimg_hyp_va x1, x2
> +
> + /* Leave idmap. */
> + br x1
> +SYM_CODE_END(__kvm_hyp_cpu_on_entry)
> +
> SYM_CODE_START(__kvm_handle_stub_hvc)
> cmp x0, #HVC_SOFT_RESTART
> b.ne 1f
> diff --git a/arch/arm64/kvm/hyp/nvhe/psci-relay.c b/arch/arm64/kvm/hyp/nvhe/psci-relay.c
> index 7aa87ab7f5ce..39e507672e6e 100644
> --- a/arch/arm64/kvm/hyp/nvhe/psci-relay.c
> +++ b/arch/arm64/kvm/hyp/nvhe/psci-relay.c
> @@ -9,12 +9,17 @@
> #include <asm/kvm_mmu.h>
> #include <kvm/arm_hypercalls.h>
> #include <linux/arm-smccc.h>
> +#include <linux/kvm_host.h>
> #include <linux/psci.h>
> #include <kvm/arm_psci.h>
> #include <uapi/linux/psci.h>
>
> #include <nvhe/trap_handler.h>
>
> +extern char __kvm_hyp_cpu_on_entry[];
> +
> +void __noreturn __host_enter(struct kvm_cpu_context *host_ctxt);
> +
> /* Config options set by the host. */
> u32 __ro_after_init kvm_host_psci_version;
> u32 __ro_after_init kvm_host_psci_function_id[PSCI_FN_MAX];
> @@ -22,6 +27,19 @@ s64 __ro_after_init hyp_physvirt_offset;
>
> #define __hyp_pa(x) ((phys_addr_t)((x)) + hyp_physvirt_offset)
>
> +#define INVALID_CPU_ID UINT_MAX
> +
> +#define CPU_UNLOCKED 0
> +#define CPU_LOCKED 1
> +
> +struct cpu_boot_args {
> + unsigned long pc;
> + unsigned long r0;
> +};
> +
> +static DEFINE_PER_CPU(atomic_t, cpu_on_lock) = ATOMIC_INIT(0);
> +static DEFINE_PER_CPU(struct cpu_boot_args, cpu_on_args);
> +
> static u64 get_psci_func_id(struct kvm_cpu_context *host_ctxt)
> {
> DECLARE_REG(u64, func_id, host_ctxt, 0);
> @@ -78,10 +96,99 @@ static __noreturn unsigned long psci_forward_noreturn(struct kvm_cpu_context *ho
> hyp_panic(); /* unreachable */
> }
>
> +static unsigned int find_cpu_id(u64 mpidr)
> +{
> + unsigned int i;
> +
> + /* Reject invalid MPIDRs */
> + if (mpidr & ~MPIDR_HWID_BITMASK)
> + return INVALID_CPU_ID;
> +
> + for (i = 0; i < NR_CPUS; i++) {

I may not have understood the flow correctly, so just asking:
This is just called for secondaries on boot right ? And the cpumasks
are setup by then ? Just trying to see if we can use cpu_possible_mask
instead of running through all 256/1k/4k cpus(ofcourse based on NR_CPUS
config)

--
Regards,
Sudeep