[PATCH v3 19/23] arm64: KVM: Move most of the fault decoding to C

Marc Zyngier
2016-02-03T18:00:12Z

The fault decoding process (including computing the IPA in the case
of a permission fault) would be much better done in C code, as we
have a reasonable infrastructure to deal with the VHE/non-VHE
differences.

Let's move the whole thing to C, including the workaround for
erratum 834220, and just patch the odd ESR_EL2 access remaining
in hyp-entry.S.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
arch/arm64/kernel/asm-offsets.c | 3 --
arch/arm64/kvm/hyp/hyp-entry.S | 69 +++------------------------------
arch/arm64/kvm/hyp/switch.c | 85 +++++++++++++++++++++++++++++++++++++++++
3 files changed, 90 insertions(+), 67 deletions(-)

diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index fffa4ac6..b0ab4e9 100644
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -110,9 +110,6 @@ int main(void)
DEFINE(CPU_USER_PT_REGS, offsetof(struct kvm_regs, regs));
DEFINE(CPU_FP_REGS, offsetof(struct kvm_regs, fp_regs));
DEFINE(VCPU_FPEXC32_EL2, offsetof(struct kvm_vcpu, arch.ctxt.sys_regs[FPEXC32_EL2]));
- DEFINE(VCPU_ESR_EL2, offsetof(struct kvm_vcpu, arch.fault.esr_el2));
- DEFINE(VCPU_FAR_EL2, offsetof(struct kvm_vcpu, arch.fault.far_el2));
- DEFINE(VCPU_HPFAR_EL2, offsetof(struct kvm_vcpu, arch.fault.hpfar_el2));
DEFINE(VCPU_HOST_CONTEXT, offsetof(struct kvm_vcpu, arch.host_cpu_context));
#endif
#ifdef CONFIG_CPU_PM
diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
index 1bdeee7..3488894 100644
--- a/arch/arm64/kvm/hyp/hyp-entry.S
+++ b/arch/arm64/kvm/hyp/hyp-entry.S
@@ -19,7 +19,6 @@

#include <asm/alternative.h>
#include <asm/assembler.h>
-#include <asm/asm-offsets.h>
#include <asm/cpufeature.h>
#include <asm/kvm_arm.h>
#include <asm/kvm_asm.h>
@@ -69,7 +68,11 @@ ENDPROC(__vhe_hyp_call)
el1_sync: // Guest trapped into EL2
save_x0_to_x3

+alternative_if_not ARM64_HAS_VIRT_HOST_EXTN
mrs x1, esr_el2
+alternative_else
+ mrs x1, esr_el1
+alternative_endif
lsr x2, x1, #ESR_ELx_EC_SHIFT

cmp x2, #ESR_ELx_EC_HVC64
@@ -105,72 +108,10 @@ el1_trap:
cmp x2, #ESR_ELx_EC_FP_ASIMD
b.eq __fpsimd_guest_restore

- cmp x2, #ESR_ELx_EC_DABT_LOW
- mov x0, #ESR_ELx_EC_IABT_LOW
- ccmp x2, x0, #4, ne
- b.ne 1f // Not an abort we care about
-
- /* This is an abort. Check for permission fault */
-alternative_if_not ARM64_WORKAROUND_834220
- and x2, x1, #ESR_ELx_FSC_TYPE
- cmp x2, #FSC_PERM
- b.ne 1f // Not a permission fault
-alternative_else
- nop // Use the permission fault path to
- nop // check for a valid S1 translation,
- nop // regardless of the ESR value.
-alternative_endif
-
- /*
- * Check for Stage-1 page table walk, which is guaranteed
- * to give a valid HPFAR_EL2.
- */
- tbnz x1, #7, 1f // S1PTW is set
-
- /* Preserve PAR_EL1 */
- mrs x3, par_el1
- stp x3, xzr, [sp, #-16]!
-
- /*
- * Permission fault, HPFAR_EL2 is invalid.
- * Resolve the IPA the hard way using the guest VA.
- * Stage-1 translation already validated the memory access rights.
- * As such, we can use the EL1 translation regime, and don't have
- * to distinguish between EL0 and EL1 access.
- */
- mrs x2, far_el2
- at s1e1r, x2
- isb
-
- /* Read result */
- mrs x3, par_el1
- ldp x0, xzr, [sp], #16 // Restore PAR_EL1 from the stack
- msr par_el1, x0
- tbnz x3, #0, 3f // Bail out if we failed the translation
- ubfx x3, x3, #12, #36 // Extract IPA
- lsl x3, x3, #4 // and present it like HPFAR
- b 2f
-
-1: mrs x3, hpfar_el2
- mrs x2, far_el2
-
-2: mrs x0, tpidr_el2
- str w1, [x0, #VCPU_ESR_EL2]
- str x2, [x0, #VCPU_FAR_EL2]
- str x3, [x0, #VCPU_HPFAR_EL2]
-
+ mrs x0, tpidr_el2
mov x1, #ARM_EXCEPTION_TRAP
b __guest_exit

- /*
- * Translation failed. Just return to the guest and
- * let it fault again. Another CPU is probably playing
- * behind our back.
- */
-3: restore_x0_to_x3
-
- eret
-
el1_irq:
save_x0_to_x3
mrs x0, tpidr_el2
diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
index e90683a..a192357 100644
--- a/arch/arm64/kvm/hyp/switch.c
+++ b/arch/arm64/kvm/hyp/switch.c
@@ -15,6 +15,7 @@
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/

+#include <linux/types.h>
#include <asm/kvm_asm.h>

#include "hyp.h"
@@ -145,6 +146,86 @@ static void __hyp_text __vgic_restore_state(struct kvm_vcpu *vcpu)
__vgic_call_restore_state()(vcpu);
}

+static bool __hyp_text __true_value(void)
+{
+ return true;
+}
+
+static bool __hyp_text __false_value(void)
+{
+ return false;
+}
+
+static hyp_alternate_select(__check_arm_834220,
+ __false_value, __true_value,
+ ARM64_WORKAROUND_834220);
+
+static bool __hyp_text __translate_far_to_hpfar(u64 far, u64 *hpfar)
+{
+ u64 par, tmp;
+
+ /*
+ * Resolve the IPA the hard way using the guest VA.
+ *
+ * Stage-1 translation already validated the memory access
+ * rights. As such, we can use the EL1 translation regime, and
+ * don't have to distinguish between EL0 and EL1 access.
+ *
+ * We do need to save/restore PAR_EL1 though, as we haven't
+ * saved the guest context yet, and we may return early...
+ */
+ par = read_sysreg(par_el1);
+ asm volatile("at s1e1r, %0" : : "r" (far));
+ isb();
+
+ tmp = read_sysreg(par_el1);
+ write_sysreg(par, par_el1);
+
+ if (unlikely(tmp & 1))
+ return false; /* Translation failed, back to guest */
+
+ /* Convert PAR to HPFAR format */
+ *hpfar = ((tmp >> 12) & ((1UL << 36) - 1)) << 4;
+ return true;
+}
+
+static bool __hyp_text __populate_fault_info(struct kvm_vcpu *vcpu)
+{
+ u64 esr = read_sysreg_el2(esr);
+ u8 ec = esr >> ESR_ELx_EC_SHIFT;
+ u64 hpfar, far;
+
+ vcpu->arch.fault.esr_el2 = esr;
+
+ if (ec != ESR_ELx_EC_DABT_LOW && ec != ESR_ELx_EC_IABT_LOW)
+ return true;
+
+ far = read_sysreg_el2(far);
+
+ /*
+ * The HPFAR can be invalid if the stage 2 fault did not
+ * happen during a stage 1 page table walk (the ESR_EL2.S1PTW
+ * bit is clear) and one of the two following cases are true:
+ * 1. The fault was due to a permission fault
+ * 2. The processor carries errata 834220
+ *
+ * Therefore, for all non S1PTW faults where we either have a
+ * permission fault or the errata workaround is enabled, we
+ * resolve the IPA using the AT instruction.
+ */
+ if (!(esr & ESR_ELx_S1PTW) &&
+ (__check_arm_834220()() || (esr & ESR_ELx_FSC_TYPE) == FSC_PERM)) {
+ if (!__translate_far_to_hpfar(far, &hpfar))
+ return false;
+ } else {
+ hpfar = read_sysreg(hpfar_el2);
+ }
+
+ vcpu->arch.fault.far_el2 = far;
+ vcpu->arch.fault.hpfar_el2 = hpfar;
+ return true;
+}
+
static int __hyp_text __guest_run(struct kvm_vcpu *vcpu)
{
struct kvm_cpu_context *host_ctxt;
@@ -176,9 +257,13 @@ static int __hyp_text __guest_run(struct kvm_vcpu *vcpu)
__debug_restore_state(vcpu, kern_hyp_va(vcpu->arch.debug_ptr), guest_ctxt);

/* Jump in the fire! */
+again:
exit_code = __guest_enter(vcpu, host_ctxt);
/* And we're baaack! */

+ if (exit_code == ARM_EXCEPTION_TRAP && !__populate_fault_info(vcpu))
+ goto again;
+
fp_enabled = __fpsimd_enabled();

__sysreg_save_guest_state(guest_ctxt);
--
2.1.4