KVM: ARM: World-switch implementation

Provides complete world-switch implementation to switch to other guests
running in non-secure modes. Includes Hyp exception handlers that
capture necessary exception information and stores the information on
the VCPU and KVM structures.

The following Hyp-ABI is also documented in the code:

Hyp-ABI: Calling HYP-mode functions from host (in SVC mode):
   Switching to Hyp mode is done through a simple HVC #0 instruction. The
   exception vector code will check that the HVC comes from VMID==0 and if
   so will push the necessary state (SPSR, lr_usr) on the Hyp stack.
   - r0 contains a pointer to a HYP function
   - r1, r2, and r3 contain arguments to the above function.
   - The HYP function will be called with its arguments in r0, r1 and r2.
   On HYP function return, we return directly to SVC.

A call to a function executing in Hyp mode is performed like the following:

        <svc code>
        ldr     r0, =BSYM(my_hyp_fn)
        ldr     r1, =my_param
        hvc #0  ; Call my_hyp_fn(my_param) from HYP mode
        <svc code>

Otherwise, the world-switch is pretty straight-forward. All state that
can be modified by the guest is first backed up on the Hyp stack and the
VCPU values is loaded onto the hardware. State, which is not loaded, but
theoretically modifiable by the guest is protected through the
virtualiation features to generate a trap and cause software emulation.
Upon guest returns, all state is restored from hardware onto the VCPU
struct and the original state is restored from the Hyp-stack onto the
hardware.

SMP support using the VMPIDR calculated on the basis of the host MPIDR
and overriding the low bits with KVM vcpu_id contributed by Marc Zyngier.

Reuse of VMIDs has been implemented by Antonios Motakis and adapated from
a separate patch into the appropriate patches introducing the
functionality. Note that the VMIDs are stored per VM as required by the ARM
architecture reference manual.

To support VFP/NEON we trap those instructions using the HPCTR. When
we trap, we switch the FPU.  After a guest exit, the VFP state is
returned to the host.  When disabling access to floating point
instructions, we also mask FPEXC_EN in order to avoid the guest
receiving Undefined instruction exceptions before we have a chance to
switch back the floating point state.  We are reusing vfp_hard_struct,
so we depend on VFPv3 being enabled in the host kernel, if not, we still
trap cp10 and cp11 in order to inject an undefined instruction exception
whenever the guest tries to use VFP/NEON. VFP/NEON developed by
Antionios Motakis and Rusty Russell.

Aborts that are permission faults, and not stage-1 page table walk, do
not report the faulting address in the HPFAR.  We have to resolve the
IPA, and store it just like the HPFAR register on the VCPU struct. If
the IPA cannot be resolved, it means another CPU is playing with the
page tables, and we simply restart the guest.  This quirk was fixed by
Marc Zyngier.
Reviewed-by: Will Deacon <will.deacon@arm.com>
Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Antonios Motakis <a.motakis@virtualopensystems.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <c.dall@virtualopensystems.com>

arch/arm/include/asm/kvm_arm.h

@@ -98,6 +98,18 @@
 #define TTBCR_T0SZ	3
 #define HTCR_MASK	(TTBCR_T0SZ | TTBCR_IRGN0 | TTBCR_ORGN0 | TTBCR_SH0)
 
+/* Hyp System Trap Register */
+#define HSTR_T(x)	(1 << x)
+#define HSTR_TTEE	(1 << 16)
+#define HSTR_TJDBX	(1 << 17)
+
+/* Hyp Coprocessor Trap Register */
+#define HCPTR_TCP(x)	(1 << x)
+#define HCPTR_TCP_MASK	(0x3fff)
+#define HCPTR_TASE	(1 << 15)
+#define HCPTR_TTA	(1 << 20)
+#define HCPTR_TCPAC	(1 << 31)
+
 /* Hyp Debug Configuration Register bits */
 #define HDCR_TDRA	(1 << 11)
 #define HDCR_TDOSA	(1 << 10)
@@ -144,6 +156,45 @@
 #else
 #define VTTBR_X		(5 - KVM_T0SZ)
 #endif
+#define VTTBR_BADDR_SHIFT (VTTBR_X - 1)
+#define VTTBR_BADDR_MASK  (((1LLU << (40 - VTTBR_X)) - 1) << VTTBR_BADDR_SHIFT)
+#define VTTBR_VMID_SHIFT  (48LLU)
+#define VTTBR_VMID_MASK	  (0xffLLU << VTTBR_VMID_SHIFT)
+
+/* Hyp Syndrome Register (HSR) bits */
+#define HSR_EC_SHIFT	(26)
+#define HSR_EC		(0x3fU << HSR_EC_SHIFT)
+#define HSR_IL		(1U << 25)
+#define HSR_ISS		(HSR_IL - 1)
+#define HSR_ISV_SHIFT	(24)
+#define HSR_ISV		(1U << HSR_ISV_SHIFT)
+#define HSR_FSC		(0x3f)
+#define HSR_FSC_TYPE	(0x3c)
+#define HSR_WNR		(1 << 6)
+
+#define FSC_FAULT	(0x04)
+#define FSC_PERM	(0x0c)
+
+/* Hyp Prefetch Fault Address Register (HPFAR/HDFAR) */
+#define HPFAR_MASK	(~0xf)
 
+#define HSR_EC_UNKNOWN	(0x00)
+#define HSR_EC_WFI	(0x01)
+#define HSR_EC_CP15_32	(0x03)
+#define HSR_EC_CP15_64	(0x04)
+#define HSR_EC_CP14_MR	(0x05)
+#define HSR_EC_CP14_LS	(0x06)
+#define HSR_EC_CP_0_13	(0x07)
+#define HSR_EC_CP10_ID	(0x08)
+#define HSR_EC_JAZELLE	(0x09)
+#define HSR_EC_BXJ	(0x0A)
+#define HSR_EC_CP14_64	(0x0C)
+#define HSR_EC_SVC_HYP	(0x11)
+#define HSR_EC_HVC	(0x12)
+#define HSR_EC_SMC	(0x13)
+#define HSR_EC_IABT	(0x20)
+#define HSR_EC_IABT_HYP	(0x21)
+#define HSR_EC_DABT	(0x24)
+#define HSR_EC_DABT_HYP	(0x25)
 
 #endif /* __ARM_KVM_ARM_H__ */

arch/arm/include/asm/kvm_host.h

@@ -21,6 +21,7 @@
 
 #include <asm/kvm.h>
 #include <asm/kvm_asm.h>
+#include <asm/fpstate.h>
 
 #define KVM_MAX_VCPUS CONFIG_KVM_ARM_MAX_VCPUS
 #define KVM_MEMORY_SLOTS 32
@@ -85,6 +86,14 @@ struct kvm_vcpu_arch {
 	u32 hxfar;		/* Hyp Data/Inst Fault Address Register */
 	u32 hpfar;		/* Hyp IPA Fault Address Register */
 
+	/* Floating point registers (VFP and Advanced SIMD/NEON) */
+	struct vfp_hard_struct vfp_guest;
+	struct vfp_hard_struct *vfp_host;
+
+	/*
+	 * Anything that is not used directly from assembly code goes
+	 * here.
+	 */
 	/* Interrupt related fields */
 	u32 irq_lines;		/* IRQ and FIQ levels */
 
@@ -93,6 +102,9 @@ struct kvm_vcpu_arch {
 
 	/* Cache some mmu pages needed inside spinlock regions */
 	struct kvm_mmu_memory_cache mmu_page_cache;
+
+	/* Detect first run of a vcpu */
+	bool has_run_once;
 };
 
 struct kvm_vm_stat {
@@ -112,6 +124,7 @@ struct kvm_one_reg;
 int kvm_arm_get_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg);
 int kvm_arm_set_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg);
 u64 kvm_call_hyp(void *hypfn, ...);
+void force_vm_exit(const cpumask_t *mask);
 
 #define KVM_ARCH_WANT_MMU_NOTIFIER
 struct kvm;

arch/arm/kernel/asm-offsets.c

@@ -13,6 +13,9 @@
 #include <linux/sched.h>
 #include <linux/mm.h>
 #include <linux/dma-mapping.h>
+#ifdef CONFIG_KVM_ARM_HOST
+#include <linux/kvm_host.h>
+#endif
 #include <asm/cacheflush.h>
 #include <asm/glue-df.h>
 #include <asm/glue-pf.h>
@@ -146,5 +149,27 @@ int main(void)
   DEFINE(DMA_BIDIRECTIONAL,	DMA_BIDIRECTIONAL);
   DEFINE(DMA_TO_DEVICE,		DMA_TO_DEVICE);
   DEFINE(DMA_FROM_DEVICE,	DMA_FROM_DEVICE);
+#ifdef CONFIG_KVM_ARM_HOST
+  DEFINE(VCPU_KVM,		offsetof(struct kvm_vcpu, kvm));
+  DEFINE(VCPU_MIDR,		offsetof(struct kvm_vcpu, arch.midr));
+  DEFINE(VCPU_CP15,		offsetof(struct kvm_vcpu, arch.cp15));
+  DEFINE(VCPU_VFP_GUEST,	offsetof(struct kvm_vcpu, arch.vfp_guest));
+  DEFINE(VCPU_VFP_HOST,		offsetof(struct kvm_vcpu, arch.vfp_host));
+  DEFINE(VCPU_REGS,		offsetof(struct kvm_vcpu, arch.regs));
+  DEFINE(VCPU_USR_REGS,		offsetof(struct kvm_vcpu, arch.regs.usr_regs));
+  DEFINE(VCPU_SVC_REGS,		offsetof(struct kvm_vcpu, arch.regs.svc_regs));
+  DEFINE(VCPU_ABT_REGS,		offsetof(struct kvm_vcpu, arch.regs.abt_regs));
+  DEFINE(VCPU_UND_REGS,		offsetof(struct kvm_vcpu, arch.regs.und_regs));
+  DEFINE(VCPU_IRQ_REGS,		offsetof(struct kvm_vcpu, arch.regs.irq_regs));
+  DEFINE(VCPU_FIQ_REGS,		offsetof(struct kvm_vcpu, arch.regs.fiq_regs));
+  DEFINE(VCPU_PC,		offsetof(struct kvm_vcpu, arch.regs.usr_regs.ARM_pc));
+  DEFINE(VCPU_CPSR,		offsetof(struct kvm_vcpu, arch.regs.usr_regs.ARM_cpsr));
+  DEFINE(VCPU_IRQ_LINES,	offsetof(struct kvm_vcpu, arch.irq_lines));
+  DEFINE(VCPU_HSR,		offsetof(struct kvm_vcpu, arch.hsr));
+  DEFINE(VCPU_HxFAR,		offsetof(struct kvm_vcpu, arch.hxfar));
+  DEFINE(VCPU_HPFAR,		offsetof(struct kvm_vcpu, arch.hpfar));
+  DEFINE(VCPU_HYP_PC,		offsetof(struct kvm_vcpu, arch.hyp_pc));
+  DEFINE(KVM_VTTBR,		offsetof(struct kvm, arch.vttbr));
+#endif
   return 0; 
 }

arch/arm/kvm/arm.c

@@ -40,6 +40,7 @@
 #include <asm/kvm_arm.h>
 #include <asm/kvm_asm.h>
 #include <asm/kvm_mmu.h>
+#include <asm/kvm_emulate.h>
 
 #ifdef REQUIRES_VIRT
 __asm__(".arch_extension	virt");
@@ -49,6 +50,10 @@ static DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stack_page);
 static struct vfp_hard_struct __percpu *kvm_host_vfp_state;
 static unsigned long hyp_default_vectors;
 
+/* The VMID used in the VTTBR */
+static atomic64_t kvm_vmid_gen = ATOMIC64_INIT(1);
+static u8 kvm_next_vmid;
+static DEFINE_SPINLOCK(kvm_vmid_lock);
 
 int kvm_arch_hardware_enable(void *garbage)
 {
@@ -276,6 +281,8 @@ int __attribute_const__ kvm_target_cpu(void)
 
 int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
 {
+	/* Force users to call KVM_ARM_VCPU_INIT */
+	vcpu->arch.target = -1;
 	return 0;
 }
 
@@ -286,6 +293,7 @@ void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu)
 void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 {
 	vcpu->cpu = cpu;
+	vcpu->arch.vfp_host = this_cpu_ptr(kvm_host_vfp_state);
 }
 
 void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
@@ -316,9 +324,199 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *v)
 	return 0;
 }
 
+/* Just ensure a guest exit from a particular CPU */
+static void exit_vm_noop(void *info)
+{
+}
+
+void force_vm_exit(const cpumask_t *mask)
+{
+	smp_call_function_many(mask, exit_vm_noop, NULL, true);
+}
+
+/**
+ * need_new_vmid_gen - check that the VMID is still valid
+ * @kvm: The VM's VMID to checkt
+ *
+ * return true if there is a new generation of VMIDs being used
+ *
+ * The hardware supports only 256 values with the value zero reserved for the
+ * host, so we check if an assigned value belongs to a previous generation,
+ * which which requires us to assign a new value. If we're the first to use a
+ * VMID for the new generation, we must flush necessary caches and TLBs on all
+ * CPUs.
+ */
+static bool need_new_vmid_gen(struct kvm *kvm)
+{
+	return unlikely(kvm->arch.vmid_gen != atomic64_read(&kvm_vmid_gen));
+}
+
+/**
+ * update_vttbr - Update the VTTBR with a valid VMID before the guest runs
+ * @kvm	The guest that we are about to run
+ *
+ * Called from kvm_arch_vcpu_ioctl_run before entering the guest to ensure the
+ * VM has a valid VMID, otherwise assigns a new one and flushes corresponding
+ * caches and TLBs.
+ */
+static void update_vttbr(struct kvm *kvm)
+{
+	phys_addr_t pgd_phys;
+	u64 vmid;
+
+	if (!need_new_vmid_gen(kvm))
+		return;
+
+	spin_lock(&kvm_vmid_lock);
+
+	/*
+	 * We need to re-check the vmid_gen here to ensure that if another vcpu
+	 * already allocated a valid vmid for this vm, then this vcpu should
+	 * use the same vmid.
+	 */
+	if (!need_new_vmid_gen(kvm)) {
+		spin_unlock(&kvm_vmid_lock);
+		return;
+	}
+
+	/* First user of a new VMID generation? */
+	if (unlikely(kvm_next_vmid == 0)) {
+		atomic64_inc(&kvm_vmid_gen);
+		kvm_next_vmid = 1;
+
+		/*
+		 * On SMP we know no other CPUs can use this CPU's or each
+		 * other's VMID after force_vm_exit returns since the
+		 * kvm_vmid_lock blocks them from reentry to the guest.
+		 */
+		force_vm_exit(cpu_all_mask);
+		/*
+		 * Now broadcast TLB + ICACHE invalidation over the inner
+		 * shareable domain to make sure all data structures are
+		 * clean.
+		 */
+		kvm_call_hyp(__kvm_flush_vm_context);
+	}
+
+	kvm->arch.vmid_gen = atomic64_read(&kvm_vmid_gen);
+	kvm->arch.vmid = kvm_next_vmid;
+	kvm_next_vmid++;
+
+	/* update vttbr to be used with the new vmid */
+	pgd_phys = virt_to_phys(kvm->arch.pgd);
+	vmid = ((u64)(kvm->arch.vmid) << VTTBR_VMID_SHIFT) & VTTBR_VMID_MASK;
+	kvm->arch.vttbr = pgd_phys & VTTBR_BADDR_MASK;
+	kvm->arch.vttbr |= vmid;
+
+	spin_unlock(&kvm_vmid_lock);
+}
+
+/*
+ * Return > 0 to return to guest, < 0 on error, 0 (and set exit_reason) on
+ * proper exit to QEMU.
+ */
+static int handle_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
+		       int exception_index)
+{
+	run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
+	return 0;
+}
+
+static int kvm_vcpu_first_run_init(struct kvm_vcpu *vcpu)
+{
+	if (likely(vcpu->arch.has_run_once))
+		return 0;
+
+	vcpu->arch.has_run_once = true;
+	return 0;
+}
+
+/**
+ * kvm_arch_vcpu_ioctl_run - the main VCPU run function to execute guest code
+ * @vcpu:	The VCPU pointer
+ * @run:	The kvm_run structure pointer used for userspace state exchange
+ *
+ * This function is called through the VCPU_RUN ioctl called from user space. It
+ * will execute VM code in a loop until the time slice for the process is used
+ * or some emulation is needed from user space in which case the function will
+ * return with return value 0 and with the kvm_run structure filled in with the
+ * required data for the requested emulation.
+ */
 int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
 {
-	return -EINVAL;
+	int ret;
+	sigset_t sigsaved;
+
+	/* Make sure they initialize the vcpu with KVM_ARM_VCPU_INIT */
+	if (unlikely(vcpu->arch.target < 0))
+		return -ENOEXEC;
+
+	ret = kvm_vcpu_first_run_init(vcpu);
+	if (ret)
+		return ret;
+
+	if (vcpu->sigset_active)
+		sigprocmask(SIG_SETMASK, &vcpu->sigset, &sigsaved);
+
+	ret = 1;
+	run->exit_reason = KVM_EXIT_UNKNOWN;
+	while (ret > 0) {
+		/*
+		 * Check conditions before entering the guest
+		 */
+		cond_resched();
+
+		update_vttbr(vcpu->kvm);
+
+		local_irq_disable();
+
+		/*
+		 * Re-check atomic conditions
+		 */
+		if (signal_pending(current)) {
+			ret = -EINTR;
+			run->exit_reason = KVM_EXIT_INTR;
+		}
+
+		if (ret <= 0 || need_new_vmid_gen(vcpu->kvm)) {
+			local_irq_enable();
+			continue;
+		}
+
+		/**************************************************************
+		 * Enter the guest
+		 */
+		trace_kvm_entry(*vcpu_pc(vcpu));
+		kvm_guest_enter();
+		vcpu->mode = IN_GUEST_MODE;
+
+		ret = kvm_call_hyp(__kvm_vcpu_run, vcpu);
+
+		vcpu->mode = OUTSIDE_GUEST_MODE;
+		kvm_guest_exit();
+		trace_kvm_exit(*vcpu_pc(vcpu));
+		/*
+		 * We may have taken a host interrupt in HYP mode (ie
+		 * while executing the guest). This interrupt is still
+		 * pending, as we haven't serviced it yet!
+		 *
+		 * We're now back in SVC mode, with interrupts
+		 * disabled.  Enabling the interrupts now will have
+		 * the effect of taking the interrupt again, in SVC
+		 * mode this time.
+		 */
+		local_irq_enable();
+
+		/*
+		 * Back from guest
+		 *************************************************************/
+
+		ret = handle_exit(vcpu, run, ret);
+	}
+
+	if (vcpu->sigset_active)
+		sigprocmask(SIG_SETMASK, &sigsaved, NULL);
+	return ret;
 }
 
 static int vcpu_interrupt_line(struct kvm_vcpu *vcpu, int number, bool level)