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Support guest writes to the TSC by enabling the "use TSC offsetting"

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execution control and writing the difference between the host TSC and
the guest TSC into the TSC offset in the VMCS upon encountering a
write.

Reviewed by:	neel
This commit is contained in:
Tycho Nightingale 2015-06-09 00:14:47 +00:00
parent cbb052dd3e
commit 277bdd9950
3 changed files with 26 additions and 4 deletions
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25
sys/amd64/vmm/intel/vmx.c
View File

@ -856,10 +856,11 @@ vmx_vminit(struct vm *vm, pmap_t pmap)
* VM exit and entry respectively. It is also restored from the
* host VMCS area on a VM exit.
*
* The TSC MSR is exposed read-only. Writes are disallowed as that
* will impact the host TSC.
* XXX Writes would be implemented with a wrmsr trap, and
* then modifying the TSC offset in the VMCS.
* The TSC MSR is exposed read-only. Writes are disallowed as
* that will impact the host TSC. If the guest does a write
* the "use TSC offsetting" execution control is enabled and the
* difference between the host TSC and the guest TSC is written
* into the TSC offset in the VMCS.
*/
if (guest_msr_rw(vmx, MSR_GSBASE) ||
guest_msr_rw(vmx, MSR_FSBASE) ||
@ -1130,6 +1131,22 @@ vmx_clear_nmi_window_exiting(struct vmx *vmx, int vcpu)
VCPU_CTR0(vmx->vm, vcpu, "Disabling NMI window exiting");
}
int
vmx_set_tsc_offset(struct vmx *vmx, int vcpu, uint64_t offset)
{
int error;
if ((vmx->cap[vcpu].proc_ctls & PROCBASED_TSC_OFFSET) == 0) {
vmx->cap[vcpu].proc_ctls |= PROCBASED_TSC_OFFSET;
vmcs_write(VMCS_PRI_PROC_BASED_CTLS, vmx->cap[vcpu].proc_ctls);
VCPU_CTR0(vmx->vm, vcpu, "Enabling TSC offsetting");
}
error = vmwrite(VMCS_TSC_OFFSET, offset);
return (error);
}
#define NMI_BLOCKING (VMCS_INTERRUPTIBILITY_NMI_BLOCKING | \
VMCS_INTERRUPTIBILITY_MOVSS_BLOCKING)
#define HWINTR_BLOCKING (VMCS_INTERRUPTIBILITY_STI_BLOCKING | \

2
sys/amd64/vmm/intel/vmx.h
View File

@ -135,6 +135,8 @@ void vmx_call_isr(uintptr_t entry);
u_long vmx_fix_cr0(u_long cr0);
u_long vmx_fix_cr4(u_long cr4);
int vmx_set_tsc_offset(struct vmx *vmx, int vcpu, uint64_t offset);
extern char vmx_exit_guest[];
#endif

3
sys/amd64/vmm/intel/vmx_msr.c
View File

@ -474,6 +474,9 @@ vmx_wrmsr(struct vmx *vmx, int vcpuid, u_int num, uint64_t val, bool *retu)
else
vm_inject_gp(vmx->vm, vcpuid);
break;
case MSR_TSC:
error = vmx_set_tsc_offset(vmx, vcpuid, val - rdtsc());
break;
default:
error = EINVAL;
break;