Re: [Xen-devel] [PATCHv4 1/2] x86/ept: invalidate guest physical mappings on VMENTER

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On 14/12/15 14:39, David Vrabel wrote:
> If a guest allocates a page and the tlbflush_timestamp on the page
> indicates that a TLB flush of the previous owner is required, only the
> linear and combined mappings are invalidated.  The guest-physical
> mappings are not invalidated.
> 
> This is currently safe because the EPT code ensures that the
> guest-physical and combined mappings are invalidated /before/ the page
> is freed.  However, this prevents us from deferring the EPT invalidate
> until after the page is freed (e.g., to defer the invalidate until the
> p2m locks are released).
> 
> The TLB flush that may be done after allocating page already causes
> the original guest to VMEXIT, thus on VMENTER we can do an INVEPT if
> one is pending.
> 
> This means __ept_sync_domain() need not do anything and the thus the
> on_selected_cpu() call does not need to wait for as long.
> 
> ept_sync_domain() now marks all PCPUs as needing to be invalidated,
> including PCPUs that the domain has not run on.  We still only IPI
> those PCPUs that are active so this does not result in any more INVEPT
> calls.
> 
> We do not attempt to track when PCPUs may have cached translations
> because the only safe way to clear this per-CPU state is if
> immediately after an invalidate the PCPU is not active (i.e., the PCPU
> is not in d->domain_dirty_cpumask).  Since we only invalidate on
> VMENTER or by IPIing active PCPUs this can never happen.
> 
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>

Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxxx>

> ---
> v4:
> - __ept_sync_domain() is a no-op -- invalidates are done before VMENTER.
> - initialize ept->invalidate to all ones so the initial invalidate is
>   always done.
> ---
>  xen/arch/x86/hvm/vmx/vmx.c         | 22 ++++++++++------------
>  xen/arch/x86/mm/p2m-ept.c          | 29 ++++++++++++++---------------
>  xen/include/asm-x86/hvm/vmx/vmcs.h |  3 +--
>  3 files changed, 25 insertions(+), 29 deletions(-)
> 
> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
> index f7c5e4f..cca35f2 100644
> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -744,24 +744,12 @@ static void vmx_ctxt_switch_from(struct vcpu *v)
>  
>  static void vmx_ctxt_switch_to(struct vcpu *v)
>  {
> -    struct domain *d = v->domain;
>      unsigned long old_cr4 = read_cr4(), new_cr4 = mmu_cr4_features;
> -    struct ept_data *ept_data = &p2m_get_hostp2m(d)->ept;
>  
>      /* HOST_CR4 in VMCS is always mmu_cr4_features. Sync CR4 now. */
>      if ( old_cr4 != new_cr4 )
>          write_cr4(new_cr4);
>  
> -    if ( paging_mode_hap(d) )
> -    {
> -        unsigned int cpu = smp_processor_id();
> -        /* Test-and-test-and-set this CPU in the EPT-is-synced mask. */
> -        if ( !cpumask_test_cpu(cpu, ept_get_synced_mask(ept_data)) &&
> -             !cpumask_test_and_set_cpu(cpu,
> -                                       ept_get_synced_mask(ept_data)) )
> -            __invept(INVEPT_SINGLE_CONTEXT, ept_get_eptp(ept_data), 0);
> -    }
> -
>      vmx_restore_guest_msrs(v);
>      vmx_restore_dr(v);
>  }
> @@ -3507,6 +3495,16 @@ void vmx_vmenter_helper(const struct cpu_user_regs 
> *regs)
>      if ( unlikely(need_flush) )
>          vpid_sync_all();
>  
> +    if ( paging_mode_hap(curr->domain) )
> +    {
> +        struct ept_data *ept = &p2m_get_hostp2m(curr->domain)->ept;
> +        unsigned int cpu = smp_processor_id();
> +
> +        if ( cpumask_test_cpu(cpu, ept->invalidate)
> +             && cpumask_test_and_clear_cpu(cpu, ept->invalidate) )
> +            __invept(INVEPT_SINGLE_CONTEXT, ept_get_eptp(ept), 0);
> +    }
> +
>   out:
>      HVMTRACE_ND(VMENTRY, 0, 1/*cycles*/, 0, 0, 0, 0, 0, 0, 0);
>  
> diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c
> index eef0372..6e0cf89 100644
> --- a/xen/arch/x86/mm/p2m-ept.c
> +++ b/xen/arch/x86/mm/p2m-ept.c
> @@ -1089,9 +1089,10 @@ static void ept_memory_type_changed(struct p2m_domain 
> *p2m)
>  
>  static void __ept_sync_domain(void *info)
>  {
> -    struct ept_data *ept = &((struct p2m_domain *)info)->ept;
> -
> -    __invept(INVEPT_SINGLE_CONTEXT, ept_get_eptp(ept), 0);
> +    /*
> +     * The invalidate will be done before VMENTER (see
> +     * vmx_vmenter_helper()).
> +     */
>  }
>  
>  void ept_sync_domain(struct p2m_domain *p2m)
> @@ -1107,16 +1108,10 @@ void ept_sync_domain(struct p2m_domain *p2m)
>      if ( nestedhvm_enabled(d) && !p2m_is_nestedp2m(p2m) )
>          p2m_flush_nestedp2m(d);
>  
> -    /*
> -     * Flush active cpus synchronously. Flush others the next time this 
> domain
> -     * is scheduled onto them. We accept the race of other CPUs adding to
> -     * the ept_synced mask before on_selected_cpus() reads it, resulting in
> -     * unnecessary extra flushes, to avoid allocating a cpumask_t on the 
> stack.
> -     */
> -    cpumask_and(ept_get_synced_mask(ept),
> -                d->domain_dirty_cpumask, &cpu_online_map);
> +    /* May need to invalidate on all PCPUs. */
> +    cpumask_setall(ept->invalidate);
>  
> -    on_selected_cpus(ept_get_synced_mask(ept),
> +    on_selected_cpus(d->domain_dirty_cpumask,
>                       __ept_sync_domain, p2m, 1);
>  }
>  
> @@ -1182,10 +1177,14 @@ int ept_p2m_init(struct p2m_domain *p2m)
>          p2m->flush_hardware_cached_dirty = ept_flush_pml_buffers;
>      }
>  
> -    if ( !zalloc_cpumask_var(&ept->synced_mask) )
> +    if ( !zalloc_cpumask_var(&ept->invalidate) )
>          return -ENOMEM;
>  
> -    on_each_cpu(__ept_sync_domain, p2m, 1);
> +    /*
> +     * Assume an initial invalidation is required, in case an EP4TA is
> +     * reused.
> +     */
> +    cpumask_setall(ept->invalidate);
>  
>      return 0;
>  }
> @@ -1193,7 +1192,7 @@ int ept_p2m_init(struct p2m_domain *p2m)
>  void ept_p2m_uninit(struct p2m_domain *p2m)
>  {
>      struct ept_data *ept = &p2m->ept;
> -    free_cpumask_var(ept->synced_mask);
> +    free_cpumask_var(ept->invalidate);
>  }
>  
>  static void ept_dump_p2m_table(unsigned char key)
> diff --git a/xen/include/asm-x86/hvm/vmx/vmcs.h 
> b/xen/include/asm-x86/hvm/vmx/vmcs.h
> index a8d4d5b..e778d86 100644
> --- a/xen/include/asm-x86/hvm/vmx/vmcs.h
> +++ b/xen/include/asm-x86/hvm/vmx/vmcs.h
> @@ -67,7 +67,7 @@ struct ept_data {
>          };
>          u64 eptp;
>      };
> -    cpumask_var_t synced_mask;
> +    cpumask_var_t invalidate;
>  };
>  
>  #define _VMX_DOMAIN_PML_ENABLED    0
> @@ -97,7 +97,6 @@ struct pi_desc {
>  #define ept_get_wl(ept)   ((ept)->ept_wl)
>  #define ept_get_asr(ept)  ((ept)->asr)
>  #define ept_get_eptp(ept) ((ept)->eptp)
> -#define ept_get_synced_mask(ept) ((ept)->synced_mask)
>  
>  #define NR_PML_ENTRIES   512
>  
> 


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