KVM: Make kvm host use the paravirt clocksource structs

This patch updates the kvm host code to use the pvclock structs.
It also makes the paravirt clock compatible with Xen.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 62 insertions, 13 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b08812d6b34c..63a77caa59f1 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -492,8 +492,8 @@ static int do_set_msr(struct kvm_vcpu *vcpu, unsigned index, u64 *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;
+        struct pvclock_wall_clock wc;
+        struct timespec now, sys, boot;
 
         if (!wall_clock)
                 return;
@@ -502,10 +502,19 @@ static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
 
         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;
+        /*
+         * The guest calculates current wall clock time by adding
+         * system time (updated by kvm_write_guest_time below) to the
+         * wall clock specified here.  guest system time equals host
+         * system time for us, thus we must fill in host boot time here.
+         */
+        now = current_kernel_time();
+        ktime_get_ts(&sys);
+        boot = ns_to_timespec(timespec_to_ns(&now) - timespec_to_ns(&sys));
+
+        wc.sec = boot.tv_sec;
+        wc.nsec = boot.tv_nsec;
+        wc.version = version;
 
         kvm_write_guest(kvm, wall_clock, &wc, sizeof(wc));
 
@@ -513,6 +522,45 @@ static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
         kvm_write_guest(kvm, wall_clock, &version, sizeof(version));
 }
 
+static uint32_t div_frac(uint32_t dividend, uint32_t divisor)
+{
+        uint32_t quotient, remainder;
+
+        /* Don't try to replace with do_div(), this one calculates
+         * "(dividend << 32) / divisor" */
+        __asm__ ( "divl %4"
+                  : "=a" (quotient), "=d" (remainder)
+                  : "0" (0), "1" (dividend), "r" (divisor) );
+        return quotient;
+}
+
+static void kvm_set_time_scale(uint32_t tsc_khz, struct pvclock_vcpu_time_info *hv_clock)
+{
+        uint64_t nsecs = 1000000000LL;
+        int32_t  shift = 0;
+        uint64_t tps64;
+        uint32_t tps32;
+
+        tps64 = tsc_khz * 1000LL;
+        while (tps64 > nsecs*2) {
+                tps64 >>= 1;
+                shift--;
+        }
+
+        tps32 = (uint32_t)tps64;
+        while (tps32 <= (uint32_t)nsecs) {
+                tps32 <<= 1;
+                shift++;
+        }
+
+        hv_clock->tsc_shift = shift;
+        hv_clock->tsc_to_system_mul = div_frac(nsecs, tps32);
+
+        pr_debug("%s: tsc_khz %u, tsc_shift %d, tsc_mul %u\n",
+                 __FUNCTION__, tsc_khz, hv_clock->tsc_shift,
+                 hv_clock->tsc_to_system_mul);
+}
+
 static void kvm_write_guest_time(struct kvm_vcpu *v)
 {
         struct timespec ts;
@@ -523,6 +571,11 @@ static void kvm_write_guest_time(struct kvm_vcpu *v)
         if ((!vcpu->time_page))
                 return;
 
+        if (unlikely(vcpu->hv_clock_tsc_khz != tsc_khz)) {
+                kvm_set_time_scale(tsc_khz, &vcpu->hv_clock);
+                vcpu->hv_clock_tsc_khz = tsc_khz;
+        }
+
         /* Keep irq disabled to prevent changes to the clock */
         local_irq_save(flags);
         kvm_get_msr(v, MSR_IA32_TIME_STAMP_COUNTER,
@@ -537,14 +590,14 @@ static void kvm_write_guest_time(struct kvm_vcpu *v)
         /*
          * 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
+         * state, we just increase by 2 at the end.
          */
-        vcpu->hv_clock.version = 2;
+        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));
+               sizeof(vcpu->hv_clock));
 
         kunmap_atomic(shared_kaddr, KM_USER0);
 
@@ -599,10 +652,6 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
                 /* ...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);
                 vcpu->arch.time_page =
                                 gfn_to_page(vcpu->kvm, data >> PAGE_SHIFT);