Re: [Xen-devel] [PATCH 5/9] x86/vvmx: Make updating shadow EPTP value more efficient

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 29/09/17 16:01, George Dunlap wrote:
> @@ -4203,13 +4197,17 @@ static void lbr_fixup(void)
>          bdw_erratum_bdf14_fixup();
>  }
>  
> -void vmx_vmenter_helper(const struct cpu_user_regs *regs)
> +int vmx_vmenter_helper(const struct cpu_user_regs *regs)

What are the semantics of this call?  The result looks boolean, and
indicates that the vmentry should be aborted?

>  {
>      struct vcpu *curr = current;
>      u32 new_asid, old_asid;
>      struct hvm_vcpu_asid *p_asid;
>      bool_t need_flush;
>  
> +    /* Shadow EPTP can't be updated here because irqs are disabled */
> +     if ( nestedhvm_vcpu_in_guestmode(curr) && 
> vcpu_nestedhvm(curr).stale_np2m )
> +         return 1;
> +
>      if ( curr->domain->arch.hvm_domain.pi_ops.do_resume )
>          curr->domain->arch.hvm_domain.pi_ops.do_resume(curr);
>  
> @@ -4270,6 +4268,8 @@ void vmx_vmenter_helper(const struct cpu_user_regs 
> *regs)
>      __vmwrite(GUEST_RIP,    regs->rip);
>      __vmwrite(GUEST_RSP,    regs->rsp);
>      __vmwrite(GUEST_RFLAGS, regs->rflags | X86_EFLAGS_MBS);
> +
> +    return 0;
>  }
>  
>  /*
> diff --git a/xen/arch/x86/hvm/vmx/vvmx.c b/xen/arch/x86/hvm/vmx/vvmx.c
> index 2f468e6ced..48e37158af 100644
> --- a/xen/arch/x86/hvm/vmx/vvmx.c
> +++ b/xen/arch/x86/hvm/vmx/vvmx.c
> @@ -1405,12 +1405,32 @@ static void virtual_vmexit(struct cpu_user_regs *regs)
>      vmsucceed(regs);
>  }
>  
> +static void nvmx_eptp_update(void)
> +{

struct vcpu *curr = current; will most likely half the compiled size of
this function.

> +    if ( !nestedhvm_vcpu_in_guestmode(current) ||
> +          vcpu_nestedhvm(current).nv_vmexit_pending ||
> +         !vcpu_nestedhvm(current).stale_np2m ||
> +         !nestedhvm_paging_mode_hap(current) )
> +        return;
> +
> +    /*
> +     * Interrupts are enabled here, so we need to clear stale_np2m
> +     * before we do the vmwrite.  If we do it in the other order, an
> +     * and IPI comes in changing the shadow eptp after the vmwrite,
> +     * we'll complete the vmenter with a stale eptp value.
> +     */
> +    vcpu_nestedhvm(current).stale_np2m = false;
> +    __vmwrite(EPT_POINTER, get_shadow_eptp(current));
> +}
> +
>  void nvmx_switch_guest(void)
>  {
>      struct vcpu *v = current;
>      struct nestedvcpu *nvcpu = &vcpu_nestedhvm(v);
>      struct cpu_user_regs *regs = guest_cpu_user_regs();
>  
> +    nvmx_eptp_update();
> +
>      /*
>       * A pending IO emulation may still be not finished. In this case, no
>       * virtual vmswitch is allowed. Or else, the following IO emulation will
> diff --git a/xen/include/asm-x86/hvm/vcpu.h b/xen/include/asm-x86/hvm/vcpu.h
> index 6c54773f1c..5cfa4b4aa4 100644
> --- a/xen/include/asm-x86/hvm/vcpu.h
> +++ b/xen/include/asm-x86/hvm/vcpu.h
> @@ -115,6 +115,7 @@ struct nestedvcpu {
>  
>      bool_t nv_flushp2m; /* True, when p2m table must be flushed */
>      struct p2m_domain *nv_p2m; /* used p2m table for this vcpu */
> +    bool stale_np2m; /* True when p2m_base in VMCX02 is no longer valid */

VMCx02 ? which helps distinguish the two parts of semantic information
encoded there, and to avoid looking like we've gained a third acronym.

~Andrew

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel