[PATCH 26/26] KVM: arm64: Parametrize exception entry with a target EL

Marc Zyngier
2020-04-22T12:21:33Z

We currently assume that an exception is delivered to EL1, always.
Once we emulate EL2, this no longer will be the case. To prepare
for this, add a target_mode parameter.

While we're at it, merge the computing of the target PC and PSTATE in
a single function that updates both PC and CPSR after saving their
previous values in the corresponding ELR/SPSR. This ensures that they
are updated in the correct order (a pretty common source of bugs...).

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
arch/arm64/kvm/inject_fault.c | 75 ++++++++++++++++++-----------------
1 file changed, 38 insertions(+), 37 deletions(-)

diff --git a/arch/arm64/kvm/inject_fault.c b/arch/arm64/kvm/inject_fault.c
index d3ebf8bca4b89..3dbcbc839b9c3 100644
--- a/arch/arm64/kvm/inject_fault.c
+++ b/arch/arm64/kvm/inject_fault.c
@@ -26,28 +26,12 @@ enum exception_type {
except_type_serror = 0x180,
};

-static u64 get_except_vector(struct kvm_vcpu *vcpu, enum exception_type type)
-{
- u64 exc_offset;
-
- switch (*vcpu_cpsr(vcpu) & (PSR_MODE_MASK | PSR_MODE32_BIT)) {
- case PSR_MODE_EL1t:
- exc_offset = CURRENT_EL_SP_EL0_VECTOR;
- break;
- case PSR_MODE_EL1h:
- exc_offset = CURRENT_EL_SP_ELx_VECTOR;
- break;
- case PSR_MODE_EL0t:
- exc_offset = LOWER_EL_AArch64_VECTOR;
- break;
- default:
- exc_offset = LOWER_EL_AArch32_VECTOR;
- }
-
- return vcpu_read_sys_reg(vcpu, VBAR_EL1) + exc_offset + type;
-}
-
/*
+ * This performs the exception entry at a given EL (@target_mode), stashing PC
+ * and PSTATE into ELR and SPSR respectively, and compute the new PC/PSTATE.
+ * The EL passed to this function *must* be a non-secure, privileged mode with
+ * bit 0 being set (PSTATE.SP == 1).
+ *
* When an exception is taken, most PSTATE fields are left unchanged in the
* handler. However, some are explicitly overridden (e.g. M[4:0]). Luckily all
* of the inherited bits have the same position in the AArch64/AArch32 SPSR_ELx
@@ -59,10 +43,35 @@ static u64 get_except_vector(struct kvm_vcpu *vcpu, enum exception_type type)
* Here we manipulate the fields in order of the AArch64 SPSR_ELx layout, from
* MSB to LSB.
*/
-static unsigned long get_except64_pstate(struct kvm_vcpu *vcpu)
+static void enter_exception(struct kvm_vcpu *vcpu, unsigned long target_mode,
+ enum exception_type type)
{
- unsigned long sctlr = vcpu_read_sys_reg(vcpu, SCTLR_EL1);
- unsigned long old, new;
+ unsigned long sctlr, vbar, old, new, mode;
+ u64 exc_offset;
+
+ mode = *vcpu_cpsr(vcpu) & (PSR_MODE_MASK | PSR_MODE32_BIT);
+
+ if (mode == target_mode)
+ exc_offset = CURRENT_EL_SP_ELx_VECTOR;
+ else if ((mode | 1) == target_mode)
+ exc_offset = CURRENT_EL_SP_EL0_VECTOR;
+ else if (!(mode & PSR_MODE32_BIT))
+ exc_offset = LOWER_EL_AArch64_VECTOR;
+ else
+ exc_offset = LOWER_EL_AArch32_VECTOR;
+
+ switch (target_mode) {
+ case PSR_MODE_EL1h:
+ vbar = vcpu_read_sys_reg(vcpu, VBAR_EL1);
+ sctlr = vcpu_read_sys_reg(vcpu, SCTLR_EL1);
+ vcpu_write_sys_reg(vcpu, *vcpu_pc(vcpu), ELR_EL1);
+ break;
+ default:
+ /* Don't do that */
+ BUG();
+ }
+
+ *vcpu_pc(vcpu) = vbar + exc_offset + type;

old = *vcpu_cpsr(vcpu);
new = 0;
@@ -105,9 +114,10 @@ static unsigned long get_except64_pstate(struct kvm_vcpu *vcpu)
new |= PSR_I_BIT;
new |= PSR_F_BIT;

- new |= PSR_MODE_EL1h;
+ new |= target_mode;

- return new;
+ *vcpu_cpsr(vcpu) = new;
+ vcpu_write_spsr(vcpu, old);
}

static void inject_abt64(struct kvm_vcpu *vcpu, bool is_iabt, unsigned long addr)
@@ -116,11 +126,7 @@ static void inject_abt64(struct kvm_vcpu *vcpu, bool is_iabt, unsigned long addr
bool is_aarch32 = vcpu_mode_is_32bit(vcpu);
u32 esr = 0;

- vcpu_write_sys_reg(vcpu, *vcpu_pc(vcpu), ELR_EL1);
- *vcpu_pc(vcpu) = get_except_vector(vcpu, except_type_sync);
-
- *vcpu_cpsr(vcpu) = get_except64_pstate(vcpu);
- vcpu_write_spsr(vcpu, cpsr);
+ enter_exception(vcpu, PSR_MODE_EL1h, except_type_sync);

vcpu_write_sys_reg(vcpu, addr, FAR_EL1);

@@ -148,14 +154,9 @@ static void inject_abt64(struct kvm_vcpu *vcpu, bool is_iabt, unsigned long addr

static void inject_undef64(struct kvm_vcpu *vcpu)
{
- unsigned long cpsr = *vcpu_cpsr(vcpu);
u32 esr = (ESR_ELx_EC_UNKNOWN << ESR_ELx_EC_SHIFT);

- vcpu_write_sys_reg(vcpu, *vcpu_pc(vcpu), ELR_EL1);
- *vcpu_pc(vcpu) = get_except_vector(vcpu, except_type_sync);
-
- *vcpu_cpsr(vcpu) = get_except64_pstate(vcpu);
- vcpu_write_spsr(vcpu, cpsr);
+ enter_exception(vcpu, PSR_MODE_EL1h, except_type_sync);

/*
* Build an unknown exception, depending on the instruction
--
2.26.1