Re: [Xen-devel] [PATCH v3] VMX: Eliminate cr3 save/loading exiting when UG enabled

["Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>]

Zhang, Yang Z wrote on 2013-12-19:
> From: Yang Zhang <yang.z.zhang@xxxxxxxxx>
> 
> With the feature of unrestricted guest, there should be no vmexit be
> triggered when guest accesses the cr3 in non-paging mode. This patch
> will clear the cr3 save/loading bit in vmcs control filed to eliminate
> cr3 access vmexit on UG avaliable hardware.
> 
> The previous patch (commit c9efe34c119418a5ac776e5d91aeefcce4576518)
> did the same thing compare to this one. But it will cause guest fail
> to boot up on non-UG hardware which is repoted by Jan and it has been
> reverted (commit 1e2bf05ec37cf04b0e01585eae524509179f165e).
> 
> This patch incorporate the fixing and guest are working well both in
> UG and non-UG platform with this patch.
> 

Hi, Jun and Andrew,

Please help to review this one which is different from the first one.
The main difference is that on non-UG hardware, guest may write cr3 before 
enabling paging. So we should not set guest_cr3 to the value of hw_cr3 which 
contain the EPT identify mapping address on non-paging mode .

> Reported-by: Jan Beulich <jbeulich@xxxxxxxx>
> Signed-off-by: Yang Zhang <yang.z.zhang@xxxxxxxxx>
> ---
> changes in v3:
> Revise the patch description according Jan's suggestion
> 
> changes in v2:
> Fix the guest boot failure on non-UG platform.
> 
> There are some discussions around the first patch, please see the
> following link: http://www.gossamer-threads.com/lists/xen/devel/302810
> 
> ---
>  xen/arch/x86/hvm/vmx/vmx.c |    9 +++++----
>  1 files changed, 5 insertions(+), 4 deletions(-)
> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
> index dfff628..f6409d6 100644 --- a/xen/arch/x86/hvm/vmx/vmx.c +++
> b/xen/arch/x86/hvm/vmx/vmx.c @@ -1157,7 +1157,7 @@ static void
> vmx_update_guest_cr(struct vcpu *v, unsigned int cr)
>              uint32_t cr3_ctls = (CPU_BASED_CR3_LOAD_EXITING |
>                                   CPU_BASED_CR3_STORE_EXITING);
>              v->arch.hvm_vmx.exec_control &= ~cr3_ctls;
> -            if ( !hvm_paging_enabled(v) )
> +            if ( !hvm_paging_enabled(v) && !vmx_unrestricted_guest(v)
> + )
>                  v->arch.hvm_vmx.exec_control |= cr3_ctls;
>              /* Trap CR3 updates if CR3 memory events are enabled. */
> @@ -1231,7 +1231,7 @@ static void vmx_update_guest_cr(struct vcpu *v,
> unsigned int cr)
>      case 3:
>          if ( paging_mode_hap(v->domain) )
>          {
> -            if ( !hvm_paging_enabled(v) )
> +            if ( !hvm_paging_enabled(v) && !vmx_unrestricted_guest(v)
> + )
>                  v->arch.hvm_vcpu.hw_cr[3] =
> v->domain->arch.hvm_domain.params[HVM_PARAM_IDENT_PT];
>              vmx_load_pdptrs(v);
> @@ -2487,10 +2487,11 @@ void vmx_vmexit_handler(struct cpu_user_regs
> *regs)
> 
>      hvm_invalidate_regs_fields(regs);
> -    if ( paging_mode_hap(v->domain) && hvm_paging_enabled(v) )
> +    if ( paging_mode_hap(v->domain) )
>      {
>          __vmread(GUEST_CR3, &v->arch.hvm_vcpu.hw_cr[3]);
> -        v->arch.hvm_vcpu.guest_cr[3] = v->arch.hvm_vcpu.hw_cr[3];
> +        if ( vmx_unrestricted_guest(v) || hvm_paging_enabled(v) )
> +            v->arch.hvm_vcpu.guest_cr[3] = v->arch.hvm_vcpu.hw_cr[3];
>      }
>      
>      __vmread(VM_EXIT_REASON, &exit_reason);


Best regards,
Yang



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