On 09/26/2010 01:14 PM, Nadav Har'El wrote:
On Mon, Jun 14, 2010, Avi Kivity wrote about "Re: [PATCH 16/24] Implement VMLAUNCH and VMRESUME": > >+ vmx_set_cr0(vcpu, > >+ (get_shadow_vmcs(vcpu)->guest_cr0& > >+ ~get_shadow_vmcs(vcpu)->cr0_guest_host_mask) | > >+ (get_shadow_vmcs(vcpu)->cr0_read_shadow& > >+ get_shadow_vmcs(vcpu)->cr0_guest_host_mask)); > >+ > >+ /* However, vmx_set_cr0 incorrectly enforces KVM's relationship > >between > >+ * GUEST_CR0 and CR0_READ_SHADOW, e.g., that the former is the same > >as > >+ * the latter with with TS added if !fpu_active. We need to take the > >+ * actual GUEST_CR0 that L1 wanted, just with added TS if !fpu_active > >+ * like KVM wants (for the "lazy fpu" feature, to avoid the costly > >+ * restoration of fpu registers until the FPU is really used). > >+ */ > >+ vmcs_writel(GUEST_CR0, get_shadow_vmcs(vcpu)->guest_cr0 | > >+ (vcpu->fpu_active ? 0 : X86_CR0_TS)); > > > > Please update vmx_set_cr0() instead. How would you like that I do that? I could split vmx_set_cr0(vcpu, cr0) into a __vmx_set_cr0(vcpu, cr0, hw_cr0) and vmx_set_cr0 that calls it. Is this what you had in mind? Won't it be a little ugly? I agree, though, that it will avoid the vmwriting GUEST_CR0 twice in the nested case.
Just move the extra calculations into vmx_set_cr0(). Check if you're in nested mode, and if so apply cr0_guest_host_mask.
The vmlaunch/vmresume code becomes kvm_set_cr0(vcpu, get_shadow_vmcs(vcpu)->guest_cr0).
> >+ /* we have to set the X86_CR0_PG bit of the cached cr0, because > >+ * kvm_mmu_reset_context enables paging only if X86_CR0_PG is set in > >+ * CR0 (we need the paging so that KVM treat this guest as a paging > >+ * guest so we can easly forward page faults to L1.) > >+ */ > >+ vcpu->arch.cr0 |= X86_CR0_PG; > > > > Since this version doesn't support unrestricted nested guests, cr0.pg > will be already set or we will have failed vmentry. I believe without this "hack", things didn't work properly during boot of L2, when cr0_read_shadow.pg was not yet set. I think PG is set in guest_cr0, but not in cr0_read_shadow, which is what vcpu->arch.cr0 caches.
I don't see how vcpu->arch.cr0 can cache cr0_read_shadow. All the mmu calculations depend on vcpu->arch.cr0, which must be what the processor uses for translations. cr0_read_shadow is only use to emulate read access to cr0 (note we need to both update the real CR0_READ_SHADOW, and to consider the virtual CR0_READ_SHADOW when emulating).
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