[PATCH v4 14/28] KVM: arm64: nv: Add trap forwarding infrastructure
Marc Zyngier
maz at kernel.org
Tue Aug 15 11:38:48 PDT 2023
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))
+);
+
#endif /* _TRACE_ARM_ARM64_KVM_H */
#undef TRACE_INCLUDE_PATH
--
2.34.1
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