[PATCH v4 14/28] KVM: arm64: nv: Add trap forwarding infrastructure

[Miguel Luis]

Hi Marc,

> On 15 Aug 2023, at 18:38, Marc Zyngier <maz at kernel.org> wrote:
> 
> A significant part of what a NV hypervisor needs to do is to decide
> whether a trap from a L2+ guest has to be forwarded to a L1 guest
> or handled locally. This is done by checking for the trap bits that
> the guest hypervisor has set and acting accordingly, as described by
> the architecture.
> 
> A previous approach was to sprinkle a bunch of checks in all the
> system register accessors, but this is pretty error prone and doesn't
> help getting an overview of what is happening.
> 
> Instead, implement a set of global tables that describe a trap bit,
> combinations of trap bits, behaviours on trap, and what bits must
> be evaluated on a system register trap.
> 
> Although this is painful to describe, this allows to specify each
> and every control bit in a static manner. To make it efficient,
> the table is inserted in an xarray that is global to the system,
> and checked each time we trap a system register while running
> a L2 guest.
> 
> Add the basic infrastructure for now, while additional patches will
> implement configuration registers.
> 
> Signed-off-by: Marc Zyngier <maz at kernel.org>
> ---
> arch/arm64/include/asm/kvm_host.h   |   1 +
> arch/arm64/include/asm/kvm_nested.h |   2 +
> arch/arm64/kvm/emulate-nested.c     | 282 ++++++++++++++++++++++++++++
> arch/arm64/kvm/sys_regs.c           |   6 +
> arch/arm64/kvm/trace_arm.h          |  26 +++
> 5 files changed, 317 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 721680da1011..cb1c5c54cedd 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -988,6 +988,7 @@ int kvm_handle_cp10_id(struct kvm_vcpu *vcpu);
> void kvm_reset_sys_regs(struct kvm_vcpu *vcpu);
> 
> int __init kvm_sys_reg_table_init(void);
> +int __init populate_nv_trap_config(void);
> 
> bool lock_all_vcpus(struct kvm *kvm);
> void unlock_all_vcpus(struct kvm *kvm);
> diff --git a/arch/arm64/include/asm/kvm_nested.h b/arch/arm64/include/asm/kvm_nested.h
> index 8fb67f032fd1..fa23cc9c2adc 100644
> --- a/arch/arm64/include/asm/kvm_nested.h
> +++ b/arch/arm64/include/asm/kvm_nested.h
> @@ -11,6 +11,8 @@ static inline bool vcpu_has_nv(const struct kvm_vcpu *vcpu)
> test_bit(KVM_ARM_VCPU_HAS_EL2, vcpu->arch.features));
> }
> 
> +extern bool __check_nv_sr_forward(struct kvm_vcpu *vcpu);
> +
> struct sys_reg_params;
> struct sys_reg_desc;
> 
> diff --git a/arch/arm64/kvm/emulate-nested.c b/arch/arm64/kvm/emulate-nested.c
> index b96662029fb1..d5837ed0077c 100644
> --- a/arch/arm64/kvm/emulate-nested.c
> +++ b/arch/arm64/kvm/emulate-nested.c
> @@ -14,6 +14,288 @@
> 
> #include "trace.h"
> 
> +enum trap_behaviour {
> + BEHAVE_HANDLE_LOCALLY = 0,
> + BEHAVE_FORWARD_READ = BIT(0),
> + BEHAVE_FORWARD_WRITE = BIT(1),
> + BEHAVE_FORWARD_ANY = BEHAVE_FORWARD_READ | BEHAVE_FORWARD_WRITE,
> +};
> +
> +struct trap_bits {
> + const enum vcpu_sysreg index;
> + const enum trap_behaviour behaviour;
> + const u64 value;
> + const u64 mask;
> +};
> +
> +/* Coarse Grained Trap definitions */
> +enum cgt_group_id {
> + /* Indicates no coarse trap control */
> + __RESERVED__,
> +
> + /*
> + * The first batch of IDs denote coarse trapping that are used
> + * on their own instead of being part of a combination of
> + * trap controls.
> + */
> +
> + /*
> + * Anything after this point is a combination of coarse trap
> + * controls, which must all be evaluated to decide what to do.
> + */
> + __MULTIPLE_CONTROL_BITS__,
> +
> + /*
> + * Anything after this point requires a callback evaluating a
> + * complex trap condition. Hopefully we'll never need this...
> + */
> + __COMPLEX_CONDITIONS__,
> +
> + /* Must be last */
> + __NR_CGT_GROUP_IDS__
> +};
> +
> +static const struct trap_bits coarse_trap_bits[] = {
> +};
> +
> +#define MCB(id, ...) \
> + [id - __MULTIPLE_CONTROL_BITS__] = \
> + (const enum cgt_group_id[]){ \
> + __VA_ARGS__, __RESERVED__ \
> + }
> +
> +static const enum cgt_group_id *coarse_control_combo[] = {
> +};
> +
> +typedef enum trap_behaviour (*complex_condition_check)(struct kvm_vcpu *);
> +
> +#define CCC(id, fn) \
> + [id - __COMPLEX_CONDITIONS__] = fn
> +
> +static const complex_condition_check ccc[] = {
> +};
> +
> +/*
> + * Bit assignment for the trap controls. We use a 64bit word with the
> + * following layout for each trapped sysreg:
> + *
> + * [9:0] enum cgt_group_id (10 bits)
> + * [62:10] Unused (53 bits)
> + * [63] RES0 - Must be zero, as lost on insertion in the xarray
> + */
> +#define TC_CGT_BITS 10
> +
> +union trap_config {
> + u64 val;
> + struct {
> + unsigned long cgt:TC_CGT_BITS; /* Coarse Grained Trap id */
> + unsigned long unused:53; /* Unused, should be zero */
> + unsigned long mbz:1; /* Must Be Zero */
> + };
> +};
> +
> +struct encoding_to_trap_config {
> + const u32 encoding;
> + const u32 end;
> + const union trap_config tc;
> + const unsigned int line;
> +};
> +
> +#define SR_RANGE_TRAP(sr_start, sr_end, trap_id) \
> + { \
> + .encoding = sr_start, \
> + .end = sr_end, \
> + .tc = { \
> + .cgt = trap_id, \
> + }, \
> + .line = __LINE__, \
> + }
> +
> +#define SR_TRAP(sr, trap_id) SR_RANGE_TRAP(sr, sr, trap_id)
> +
> +/*
> + * Map encoding to trap bits for exception reported with EC=0x18.
> + * These must only be evaluated when running a nested hypervisor, but
> + * that the current context is not a hypervisor context. When the
> + * trapped access matches one of the trap controls, the exception is
> + * re-injected in the nested hypervisor.
> + */
> +static const struct encoding_to_trap_config encoding_to_cgt[] __initconst = {
> +};
> +
> +static DEFINE_XARRAY(sr_forward_xa);
> +
> +static union trap_config get_trap_config(u32 sysreg)
> +{
> + return (union trap_config) {
> + .val = xa_to_value(xa_load(&sr_forward_xa, sysreg)),
> + };
> +}
> +
> +static __init void print_nv_trap_error(const struct encoding_to_trap_config *tc,
> +       const char *type, int err)
> +{
> + kvm_err("%s line %d encoding range "
> + "(%d, %d, %d, %d, %d) - (%d, %d, %d, %d, %d) (err=%d)\n",
> + type, tc->line,
> + sys_reg_Op0(tc->encoding), sys_reg_Op1(tc->encoding),
> + sys_reg_CRn(tc->encoding), sys_reg_CRm(tc->encoding),
> + sys_reg_Op2(tc->encoding),
> + sys_reg_Op0(tc->end), sys_reg_Op1(tc->end),
> + sys_reg_CRn(tc->end), sys_reg_CRm(tc->end),
> + sys_reg_Op2(tc->end),
> + err);
> +}
> +
> +int __init populate_nv_trap_config(void)
> +{
> + int ret = 0;
> +
> + BUILD_BUG_ON(sizeof(union trap_config) != sizeof(void *));
> + BUILD_BUG_ON(__NR_CGT_GROUP_IDS__ > BIT(TC_CGT_BITS));
> +
> + for (int i = 0; i < ARRAY_SIZE(encoding_to_cgt); i++) {
> + const struct encoding_to_trap_config *cgt = &encoding_to_cgt[i];
> + void *prev;
> +
> + if (cgt->tc.val & BIT(63)) {
> + kvm_err("CGT[%d] has MBZ bit set\n", i);
> + ret = -EINVAL;
> + }
> +
> + if (cgt->encoding != cgt->end) {
> + prev = xa_store_range(&sr_forward_xa,
> +      cgt->encoding, cgt->end,
> +      xa_mk_value(cgt->tc.val),
> +      GFP_KERNEL);
> + } else {
> + prev = xa_store(&sr_forward_xa, cgt->encoding,
> + xa_mk_value(cgt->tc.val), GFP_KERNEL);
> + if (prev && !xa_is_err(prev)) {
> + ret = -EINVAL;
> + print_nv_trap_error(cgt, "Duplicate CGT", ret);
> + }
> + }
> +
> + if (xa_is_err(prev)) {
> + ret = xa_err(prev);
> + print_nv_trap_error(cgt, "Failed CGT insertion", ret);
> + }
> + }
> +
> + kvm_info("nv: %ld coarse grained trap handlers\n",
> + ARRAY_SIZE(encoding_to_cgt));
> +
> + for (int id = __MULTIPLE_CONTROL_BITS__; id < __COMPLEX_CONDITIONS__; id++) {
> + const enum cgt_group_id *cgids;
> +
> + cgids = coarse_control_combo[id - __MULTIPLE_CONTROL_BITS__];
> +
> + for (int i = 0; cgids[i] != __RESERVED__; i++) {
> + if (cgids[i] >= __MULTIPLE_CONTROL_BITS__) {
> + kvm_err("Recursive MCB %d/%d\n", id, cgids[i]);
> + ret = -EINVAL;
> + }
> + }
> + }
> +
> + if (ret)
> + xa_destroy(&sr_forward_xa);
> +
> + return ret;
> +}
> +
> +static enum trap_behaviour get_behaviour(struct kvm_vcpu *vcpu,
> + const struct trap_bits *tb)
> +{
> + enum trap_behaviour b = BEHAVE_HANDLE_LOCALLY;
> + u64 val;
> +
> + val = __vcpu_sys_reg(vcpu, tb->index);
> + if ((val & tb->mask) == tb->value)
> + b |= tb->behaviour;
> +
> + return b;
> +}
> +
> +static enum trap_behaviour __compute_trap_behaviour(struct kvm_vcpu *vcpu,
> +    const enum cgt_group_id id,
> +    enum trap_behaviour b)
> +{
> + switch (id) {
> + const enum cgt_group_id *cgids;
> +
> + case __RESERVED__ ... __MULTIPLE_CONTROL_BITS__ - 1:
> + if (likely(id != __RESERVED__))
> + b |= get_behaviour(vcpu, &coarse_trap_bits[id]);
> + break;
> + case __MULTIPLE_CONTROL_BITS__ ... __COMPLEX_CONDITIONS__ - 1:
> + /* Yes, this is recursive. Don't do anything stupid. */
> + cgids = coarse_control_combo[id - __MULTIPLE_CONTROL_BITS__];
> + for (int i = 0; cgids[i] != __RESERVED__; i++)
> + b |= __compute_trap_behaviour(vcpu, cgids[i], b);
> + break;
> + default:
> + if (ARRAY_SIZE(ccc))
> + b |= ccc[id -  __COMPLEX_CONDITIONS__](vcpu);
> + break;
> + }
> +
> + return b;
> +}
> +
> +static enum trap_behaviour compute_trap_behaviour(struct kvm_vcpu *vcpu,
> +  const union trap_config tc)
> +{
> + enum trap_behaviour b = BEHAVE_HANDLE_LOCALLY;
> +
> + return __compute_trap_behaviour(vcpu, tc.cgt, b);
> +}
> +
> +bool __check_nv_sr_forward(struct kvm_vcpu *vcpu)
> +{
> + union trap_config tc;
> + enum trap_behaviour b;
> + bool is_read;
> + u32 sysreg;
> + u64 esr;
> +
> + if (!vcpu_has_nv(vcpu) || is_hyp_ctxt(vcpu))
> + return false;
> +
> + esr = kvm_vcpu_get_esr(vcpu);
> + sysreg = esr_sys64_to_sysreg(esr);
> + is_read = (esr & ESR_ELx_SYS64_ISS_DIR_MASK) == ESR_ELx_SYS64_ISS_DIR_READ;
> +
> + tc = get_trap_config(sysreg);
> +
> + /*
> + * A value of 0 for the whole entry means that we know nothing
> + * for this sysreg, and that it cannot be re-injected into the
> + * nested hypervisor. In this situation, let's cut it short.
> + *
> + * Note that ultimately, we could also make use of the xarray
> + * to store the index of the sysreg in the local descriptor
> + * array, avoiding another search... Hint, hint...
> + */
> + if (!tc.val)
> + return false;
> +
> + b = compute_trap_behaviour(vcpu, tc);
> +
> + if (((b & BEHAVE_FORWARD_READ) && is_read) ||
> +    ((b & BEHAVE_FORWARD_WRITE) && !is_read))
> + goto inject;
> +
> + return false;
> +
> +inject:
> + trace_kvm_forward_sysreg_trap(vcpu, sysreg, is_read);
> +
> + kvm_inject_nested_sync(vcpu, kvm_vcpu_get_esr(vcpu));
> + return true;
> +}
> +
> static u64 kvm_check_illegal_exception_return(struct kvm_vcpu *vcpu, u64 spsr)
> {
> u64 mode = spsr & PSR_MODE_MASK;
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index f5baaa508926..9556896311db 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -3177,6 +3177,9 @@ int kvm_handle_sys_reg(struct kvm_vcpu *vcpu)
> 
> trace_kvm_handle_sys_reg(esr);
> 
> + if (__check_nv_sr_forward(vcpu))
> + return 1;
> +
> params = esr_sys64_to_params(esr);
> params.regval = vcpu_get_reg(vcpu, Rt);
> 
> @@ -3594,5 +3597,8 @@ int __init kvm_sys_reg_table_init(void)
> if (!first_idreg)
> return -EINVAL;
> 
> + if (kvm_get_mode() == KVM_MODE_NV)
> + return populate_nv_trap_config();
> +
> return 0;
> }
> diff --git a/arch/arm64/kvm/trace_arm.h b/arch/arm64/kvm/trace_arm.h
> index 6ce5c025218d..8ad53104934d 100644
> --- a/arch/arm64/kvm/trace_arm.h
> +++ b/arch/arm64/kvm/trace_arm.h
> @@ -364,6 +364,32 @@ TRACE_EVENT(kvm_inject_nested_exception,
>  __entry->hcr_el2)
> );
> 
> +TRACE_EVENT(kvm_forward_sysreg_trap,
> +    TP_PROTO(struct kvm_vcpu *vcpu, u32 sysreg, bool is_read),
> +    TP_ARGS(vcpu, sysreg, is_read),
> +
> +    TP_STRUCT__entry(
> + __field(u64, pc)
> + __field(u32, sysreg)
> + __field(bool, is_read)
> +    ),
> +
> +    TP_fast_assign(
> + __entry->pc = *vcpu_pc(vcpu);
> + __entry->sysreg = sysreg;
> + __entry->is_read = is_read;
> +    ),
> +
> +    TP_printk("%llx %c (%d,%d,%d,%d,%d)",
> +      __entry->pc,
> +      __entry->is_read ? 'R' : 'W',
> +      sys_reg_Op0(__entry->sysreg),
> +      sys_reg_Op1(__entry->sysreg),
> +      sys_reg_CRn(__entry->sysreg),
> +      sys_reg_CRm(__entry->sysreg),
> +      sys_reg_Op2(__entry->sysreg))
> +);
> +

Reviewed-by: Miguel Luis <miguel.luis at oracle.com>

Thanks
Miguel

> #endif /* _TRACE_ARM_ARM64_KVM_H */
> 
> #undef TRACE_INCLUDE_PATH
> -- 
> 2.34.1
>