Re: [Xen-devel] [PATCH RFC v13 06/20] pvh: vmx-specific changes

[Tim Deegan <tim@xxxxxxx>]

At 17:06 +0100 on 07 Oct (1381165615), George Dunlap wrote:
> On 07/10/13 16:55, Roger Pau Monné wrote:
> >On 23/09/13 18:49, George Dunlap wrote:
> >>@@ -1028,12 +1129,28 @@ static int construct_vmcs(struct vcpu *v)
> >>                | (1U << TRAP_no_device);
> >>      vmx_update_exception_bitmap(v);
> >>  
> >>+    /* In HVM domains, this happens on the realmode->paging
> >>+     * transition.  Since PVH never goes through this transition, we
> >>+     * need to do it at start-of-day. */
> >>+    if ( is_pvh_domain(d) )
> >>+        vmx_update_debug_state(v);
> >>+
> >>      v->arch.hvm_vcpu.guest_cr[0] = X86_CR0_PE | X86_CR0_ET;
> >>+
> >>+    /* PVH domains always start in paging mode */
> >>+    if ( is_pvh_domain(d) )
> >>+        v->arch.hvm_vcpu.guest_cr[0] |= X86_CR0_PG | X86_CR0_NE | 
> >>X86_CR0_WP;
> >>+
> >>      hvm_update_guest_cr(v, 0);
> >>  
> >>-    v->arch.hvm_vcpu.guest_cr[4] = 0;
> >>+    v->arch.hvm_vcpu.guest_cr[4] = is_pvh_domain(d) ?
> >>+        real_cr4_to_pv_guest_cr4(mmu_cr4_features)
> >Here we need to mask the bits in CR4 that the guest isn't allowed to
> >set. Right now Xen is setting the VMXE bit by default, which the guest
> >is not able to modify, so if the guests tries to update CR4 based on the
> >previous value Xen is going to complain:
> >
> >+        real_cr4_to_pv_guest_cr4(mmu_cr4_features) &
> >+        ~HVM_CR4_GUEST_RESERVED_BITS(v)
> 
> Thanks for testing that -- I'll include it in the next spin-up.

<harping on> This is the sort of thing that would be easier if PVH guests
were just HVM ones with extra hypercalls. <harping off>

Tim.

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