KVM: paravirtualized clocksource: host part

This is the host part of kvm clocksource implementation. As it does
not include clockevents, it is a fairly simple implementation. We
only have to register a per-vcpu area, and start writing to it periodically.

The area is binary compatible with xen, as we use the same shadow_info
structure.

[marcelo: fix bad_page on MSR_KVM_SYSTEM_TIME]
[avi: save full value of the msr, even if enable bit is clear]
[avi: clear previous value of time_page]

Signed-off-by: Glauber de Oliveira Costa <gcosta@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

4 files changed, 145 insertions, 1 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0c910c774a9b..256c0fc92b67 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -19,6 +19,7 @@
 #include "irq.h"
 #include "mmu.h"
 
+#include <linux/clocksource.h>
 #include <linux/kvm.h>
 #include <linux/fs.h>
 #include <linux/vmalloc.h>
@@ -424,7 +425,7 @@ static u32 msrs_to_save[] = {
 #ifdef CONFIG_X86_64
         MSR_CSTAR, MSR_KERNEL_GS_BASE, MSR_SYSCALL_MASK, MSR_LSTAR,
 #endif
-        MSR_IA32_TIME_STAMP_COUNTER,
+        MSR_IA32_TIME_STAMP_COUNTER, MSR_KVM_SYSTEM_TIME, MSR_KVM_WALL_CLOCK,
 };
 
 static unsigned num_msrs_to_save;
@@ -482,6 +483,70 @@ static int do_set_msr(struct kvm_vcpu *vcpu, unsigned index, u64 *data)
         return kvm_set_msr(vcpu, index, *data);
 }
 
+static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
+{
+        static int version;
+        struct kvm_wall_clock wc;
+        struct timespec wc_ts;
+
+        if (!wall_clock)
+                return;
+
+        version++;
+
+        down_read(&kvm->slots_lock);
+        kvm_write_guest(kvm, wall_clock, &version, sizeof(version));
+
+        wc_ts = current_kernel_time();
+        wc.wc_sec = wc_ts.tv_sec;
+        wc.wc_nsec = wc_ts.tv_nsec;
+        wc.wc_version = version;
+
+        kvm_write_guest(kvm, wall_clock, &wc, sizeof(wc));
+
+        version++;
+        kvm_write_guest(kvm, wall_clock, &version, sizeof(version));
+        up_read(&kvm->slots_lock);
+}
+
+static void kvm_write_guest_time(struct kvm_vcpu *v)
+{
+        struct timespec ts;
+        unsigned long flags;
+        struct kvm_vcpu_arch *vcpu = &v->arch;
+        void *shared_kaddr;
+
+        if ((!vcpu->time_page))
+                return;
+
+        /* Keep irq disabled to prevent changes to the clock */
+        local_irq_save(flags);
+        kvm_get_msr(v, MSR_IA32_TIME_STAMP_COUNTER,
+                          &vcpu->hv_clock.tsc_timestamp);
+        ktime_get_ts(&ts);
+        local_irq_restore(flags);
+
+        /* With all the info we got, fill in the values */
+
+        vcpu->hv_clock.system_time = ts.tv_nsec +
+                                     (NSEC_PER_SEC * (u64)ts.tv_sec);
+        /*
+         * The interface expects us to write an even number signaling that the
+         * update is finished. Since the guest won't see the intermediate
+         * state, we just write "2" at the end
+         */
+        vcpu->hv_clock.version = 2;
+
+        shared_kaddr = kmap_atomic(vcpu->time_page, KM_USER0);
+
+        memcpy(shared_kaddr + vcpu->time_offset, &vcpu->hv_clock,
+                sizeof(vcpu->hv_clock));
+
+        kunmap_atomic(shared_kaddr, KM_USER0);
+
+        mark_page_dirty(v->kvm, vcpu->time >> PAGE_SHIFT);
+}
+
 
 int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
 {
@@ -511,6 +576,44 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
         case MSR_IA32_MISC_ENABLE:
                 vcpu->arch.ia32_misc_enable_msr = data;
                 break;
+        case MSR_KVM_WALL_CLOCK:
+                vcpu->kvm->arch.wall_clock = data;
+                kvm_write_wall_clock(vcpu->kvm, data);
+                break;
+        case MSR_KVM_SYSTEM_TIME: {
+                if (vcpu->arch.time_page) {
+                        kvm_release_page_dirty(vcpu->arch.time_page);
+                        vcpu->arch.time_page = NULL;
+                }
+
+                vcpu->arch.time = data;
+
+                /* we verify if the enable bit is set... */
+                if (!(data & 1))
+                        break;
+
+                /* ...but clean it before doing the actual write */
+                vcpu->arch.time_offset = data & ~(PAGE_MASK | 1);
+
+                vcpu->arch.hv_clock.tsc_to_system_mul =
+                                        clocksource_khz2mult(tsc_khz, 22);
+                vcpu->arch.hv_clock.tsc_shift = 22;
+
+                down_read(&current->mm->mmap_sem);
+                down_read(&vcpu->kvm->slots_lock);
+                vcpu->arch.time_page =
+                                gfn_to_page(vcpu->kvm, data >> PAGE_SHIFT);
+                up_read(&vcpu->kvm->slots_lock);
+                up_read(&current->mm->mmap_sem);
+
+                if (is_error_page(vcpu->arch.time_page)) {
+                        kvm_release_page_clean(vcpu->arch.time_page);
+                        vcpu->arch.time_page = NULL;
+                }
+
+                kvm_write_guest_time(vcpu);
+                break;
+        }
         default:
                 pr_unimpl(vcpu, "unhandled wrmsr: 0x%x data %llx\n", msr, data);
                 return 1;
@@ -569,6 +672,12 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
         case MSR_EFER:
                 data = vcpu->arch.shadow_efer;
                 break;
+        case MSR_KVM_WALL_CLOCK:
+                data = vcpu->kvm->arch.wall_clock;
+                break;
+        case MSR_KVM_SYSTEM_TIME:
+                data = vcpu->arch.time;
+                break;
         default:
                 pr_unimpl(vcpu, "unhandled rdmsr: 0x%x\n", msr);
                 return 1;
@@ -696,6 +805,7 @@ int kvm_dev_ioctl_check_extension(long ext)
         case KVM_CAP_USER_MEMORY:
         case KVM_CAP_SET_TSS_ADDR:
         case KVM_CAP_EXT_CPUID:
+        case KVM_CAP_CLOCKSOURCE:
                 r = 1;
                 break;
         case KVM_CAP_VAPIC:
@@ -771,6 +881,7 @@ out:
 void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 {
         kvm_x86_ops->vcpu_load(vcpu, cpu);
+        kvm_write_guest_time(vcpu);
 }
 
 void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
diff --git a/include/asm-x86/kvm_host.h b/include/asm-x86/kvm_host.h
index 623249890a0b..90c80fd830fc 100644
--- a/include/asm-x86/kvm_host.h
+++ b/include/asm-x86/kvm_host.h
@@ -262,6 +262,11 @@ struct kvm_vcpu_arch {
         /* emulate context */
 
         struct x86_emulate_ctxt emulate_ctxt;
+
+        gpa_t time;
+        struct kvm_vcpu_time_info hv_clock;
+        unsigned int time_offset;
+        struct page *time_page;
 };
 
 struct kvm_mem_alias {
@@ -288,6 +293,8 @@ struct kvm_arch{
         int round_robin_prev_vcpu;
         unsigned int tss_addr;
         struct page *apic_access_page;
+
+        gpa_t wall_clock;
 };
 
 struct kvm_vm_stat {
diff --git a/include/asm-x86/kvm_para.h b/include/asm-x86/kvm_para.h
index c6f3fd8d8c53..5ab7d3dbd357 100644
--- a/include/asm-x86/kvm_para.h
+++ b/include/asm-x86/kvm_para.h
@@ -10,10 +10,35 @@
  * paravirtualization, the appropriate feature bit should be checked.
  */
 #define KVM_CPUID_FEATURES      0x40000001
+#define KVM_FEATURE_CLOCKSOURCE 0
+
+#define MSR_KVM_WALL_CLOCK  0x11
+#define MSR_KVM_SYSTEM_TIME 0x12
 
 #ifdef __KERNEL__
 #include <asm/processor.h>
 
+/* xen binary-compatible interface. See xen headers for details */
+struct kvm_vcpu_time_info {
+        uint32_t version;
+        uint32_t pad0;
+        uint64_t tsc_timestamp;
+        uint64_t system_time;
+        uint32_t tsc_to_system_mul;
+        int8_t   tsc_shift;
+        int8_t   pad[3];
+} __attribute__((__packed__)); /* 32 bytes */
+
+struct kvm_wall_clock {
+        uint32_t wc_version;
+        uint32_t wc_sec;
+        uint32_t wc_nsec;
+} __attribute__((__packed__));
+
+
+extern void kvmclock_init(void);
+
+
 /* This instruction is vmcall.  On non-VT architectures, it will generate a
  * trap that we will then rewrite to the appropriate instruction.
  */
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index c1ec04fd000d..94540b3c6872 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -233,6 +233,7 @@ struct kvm_vapic_addr {
 #define KVM_CAP_SET_TSS_ADDR 4
 #define KVM_CAP_VAPIC 6
 #define KVM_CAP_EXT_CPUID 7
+#define KVM_CAP_CLOCKSOURCE 8
 
 /*
  * ioctls for VM fds