Hi Zhao,
On Thu, Mar 06, 2008 at 09:15:59PM +0800, Zhao Forrest wrote:
> > @@ -1219,53 +1229,75 @@ static void nonpaging_prefetch_page(struct kvm_vcpu
> > *vcpu,
> >
> > static void mmu_free_roots(struct kvm_vcpu *vcpu)
> > {
> > - int i;
> > + int i, j;
> > struct kvm_mmu_page *sp;
> >
> > - if (!VALID_PAGE(vcpu->arch.mmu.root_hpa))
> > - return;
> > + /*
> > + * Skip to the next cr3 filter entry and free it (if it's occupied).
> > + */
> > + vcpu->arch.cr3_cache_idx++;
> > + if (unlikely(vcpu->arch.cr3_cache_idx >=
> > vcpu->arch.cr3_cache_limit))
> > + vcpu->arch.cr3_cache_idx = 0;
> > +
> > + j = vcpu->arch.cr3_cache_idx;
> > + /*
> > + * Clear the guest-visible entry.
> > + */
> > + if (vcpu->arch.cr3_cache) {
> > + vcpu->arch.cr3_cache->entry[j].guest_cr3 = 0;
> > + vcpu->arch.cr3_cache->entry[j].host_cr3 = 0;
> > + }
> Here CR3_TARGET_VALUEx is not written.
> ......
> > @@ -1322,10 +1353,23 @@ static void vmx_set_cr0(struct kvm_vcpu *vcpu,
> > unsigned long cr0)
> >
> > static void vmx_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
> > {
> > + struct kvm_cr3_cache *cache;
> > + int idx;
> > +
> > vmx_flush_tlb(vcpu);
> > vmcs_writel(GUEST_CR3, cr3);
> > if (vcpu->arch.cr0 & X86_CR0_PE)
> > vmx_fpu_deactivate(vcpu);
> > +
> > + if (!vcpu->arch.cr3_cache)
> > + return;
> > +
> > + idx = vcpu->arch.cr3_cache_idx;
> > + cache = vcpu->arch.cr3_cache;
> > +
> > + cache->entry[idx].host_cr3 = cr3;
> > + cache->entry[idx].guest_cr3 = vcpu->arch.cr3;
> > + vmcs_writel(CR3_TARGET_VALUE0 + idx*2, cr3);
> > }
> >
> Here CR3_TARGET_VALUEx is written.
> My question is:
> 1 why is vmcs_writel(CR3_TARGET_VALUE0 + idx*2, cr3); called by
> vmx_set_cr3(), but not called by mmu_free_roots()?
By clearing guest_cr3 entry of the shared area we avoid the guest from
using it.
So its unecessary to also clear the corresponding CR3_TARGET_VALUE0
register.
> 2 since "cache" is also mapped to guest OS. Is calling
> vmcs_writel(CR3_TARGET_VALUE0 + idx*2, cr3); necessary?
As said above, no, because the guest will check
cache->entry[idx].guest_cr3 before attempting to use a cached host_cr3
value.
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