2010-08-20 08:08:11

by Zachary Amsden

Subject: [KVM timekeeping 01/35] Drop vm_init_tsc

This is used only by the VMX code, and is not done properly;
if the TSC is indeed backwards, it is out of sync, and will
need proper handling in the logic at each and every CPU change.
For now, drop this test during init as misguided.

Signed-off-by: Zachary Amsden <[email protected]>
---
arch/x86/include/asm/kvm_host.h | 1 -
arch/x86/kvm/vmx.c | 10 +++-------
arch/x86/kvm/x86.c | 2 --
3 files changed, 3 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 502e53f..960f9c9 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -394,7 +394,6 @@ struct kvm_arch {
gpa_t ept_identity_map_addr;

unsigned long irq_sources_bitmap;
- u64 vm_init_tsc;
s64 kvmclock_offset;

struct kvm_xen_hvm_config xen_hvm_config;
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index cf56462..a8753e1 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2518,7 +2518,7 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx)
{
u32 host_sysenter_cs, msr_low, msr_high;
u32 junk;
- u64 host_pat, tsc_this, tsc_base;
+ u64 host_pat, tsc_this;
unsigned long a;
struct desc_ptr dt;
int i;
@@ -2659,12 +2659,8 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx)
vmx->vcpu.arch.cr4_guest_owned_bits |= X86_CR4_PGE;
vmcs_writel(CR4_GUEST_HOST_MASK, ~vmx->vcpu.arch.cr4_guest_owned_bits);

- tsc_base = vmx->vcpu.kvm->arch.vm_init_tsc;
- rdtscll(tsc_this);
- if (tsc_this < vmx->vcpu.kvm->arch.vm_init_tsc)
- tsc_base = tsc_this;
-
- guest_write_tsc(0, tsc_base);
+ tsc_this = native_read_tsc();
+ guest_write_tsc(0, tsc_this);

return 0;
}
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d5ac966..1bf9227 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5495,8 +5495,6 @@ struct kvm *kvm_arch_create_vm(void)
/* Reserve bit 0 of irq_sources_bitmap for userspace irq source */
set_bit(KVM_USERSPACE_IRQ_SOURCE_ID, &kvm->arch.irq_sources_bitmap);

- rdtscll(kvm->arch.vm_init_tsc);
-
return kvm;
}

--
1.7.1

2010-08-20 16:55:02

by Glauber Costa

Subject: Re: [KVM timekeeping 01/35] Drop vm_init_tsc

On Thu, Aug 19, 2010 at 10:07:15PM -1000, Zachary Amsden wrote:
> This is used only by the VMX code, and is not done properly;
> if the TSC is indeed backwards, it is out of sync, and will
> need proper handling in the logic at each and every CPU change.
> For now, drop this test during init as misguided.
>
> Signed-off-by: Zachary Amsden <[email protected]>

Ok, not a big loose, I agree.

Btw, I suggest we start merging some of those simple
and self-contained patches, before the series grows too big.
Makes it easier for everyone to review the real important stuff.