Re: [PATCH RFC 39/55] x86: switch root_pgt to mfn_t and use new APIs

["Nuernberger, Stefan" <snu@amazon.de>]

On Thu, 2019-02-07 at 16:44 +0000, Wei Liu wrote:
> This then requires moving declaration of root page table mfn into
> mm.h
> and modify setup_cpu_root_pgt to have a single exit path.
> 
> We also need to force map_domain_page to use direct map when
> switching
> per-domain mappings. This is contrary to our end goal of removing
> direct map, but this will be removed once we make map_domain_page
> context-switch safe in another (large) patch series.
> 
> Signed-off-by: Wei Liu <wei.liu2@citrix.com>
> ---
>  xen/arch/x86/domain.c           | 15 ++++++++++++---
>  xen/arch/x86/domain_page.c      |  2 +-
>  xen/arch/x86/mm.c               |  2 +-
>  xen/arch/x86/pv/domain.c        |  2 +-
>  xen/arch/x86/smpboot.c          | 40 +++++++++++++++++++++++++++--
> -----------
>  xen/include/asm-x86/mm.h        |  2 ++
>  xen/include/asm-x86/processor.h |  1 -
>  7 files changed, 44 insertions(+), 20 deletions(-)
> 
> diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
> index 32dc4253ff..603495e55a 100644
> --- a/xen/arch/x86/domain.c
> +++ b/xen/arch/x86/domain.c
> @@ -68,6 +68,7 @@
>  #include <asm/pv/domain.h>
>  #include <asm/pv/mm.h>
>  #include <asm/spec_ctrl.h>
> +#include <asm/setup.h>
>  
>  DEFINE_PER_CPU(struct vcpu *, curr_vcpu);
>  
> @@ -1589,12 +1590,20 @@ void paravirt_ctxt_switch_from(struct vcpu
> *v)
>  
>  void paravirt_ctxt_switch_to(struct vcpu *v)
>  {
> -    root_pgentry_t *root_pgt = this_cpu(root_pgt);
> +    mfn_t rpt_mfn = this_cpu(root_pgt_mfn);
>  
> -    if ( root_pgt )
> -        root_pgt[root_table_offset(PERDOMAIN_VIRT_START)] =
> +    if ( !mfn_eq(rpt_mfn, INVALID_MFN) )
> +    {
> +        root_pgentry_t *rpt;
> +
> +        mapcache_override_current(INVALID_VCPU);

Can you elaborate why this is required? A comment might help. I assume
this forces the root pt to be mapped in idle domain context instead of
current vcpu?

- Stefan

> +        rpt = map_xen_pagetable_new(rpt_mfn);
> +        rpt[root_table_offset(PERDOMAIN_VIRT_START)] =
>              l4e_from_page(v->domain->arch.perdomain_l3_pg,
>                            __PAGE_HYPERVISOR_RW);
> +        UNMAP_XEN_PAGETABLE_NEW(rpt);
> +        mapcache_override_current(NULL);
> +    }
>  
>      if ( unlikely(v->arch.dr7 & DR7_ACTIVE_MASK) )
>          activate_debugregs(v);
> diff --git a/xen/arch/x86/domain_page.c b/xen/arch/x86/domain_page.c
> index 24083e9a86..cfcffd35f3 100644
> --- a/xen/arch/x86/domain_page.c
> +++ b/xen/arch/x86/domain_page.c
> @@ -57,7 +57,7 @@ static inline struct vcpu
> *mapcache_current_vcpu(void)
>      return v;
>  }
>  
> -void __init mapcache_override_current(struct vcpu *v)
> +void mapcache_override_current(struct vcpu *v)
>  {
>      this_cpu(override) = v;
>  }
> diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
> index 9e115ef0b8..44c9df5c9e 100644
> --- a/xen/arch/x86/mm.c
> +++ b/xen/arch/x86/mm.c
> @@ -564,7 +564,7 @@ void write_ptbase(struct vcpu *v)
>      if ( is_pv_vcpu(v) && v->domain->arch.pv.xpti )
>      {
>          cpu_info->root_pgt_changed = true;
> -        cpu_info->pv_cr3 = __pa(this_cpu(root_pgt));
> +        cpu_info->pv_cr3 = mfn_to_maddr(this_cpu(root_pgt_mfn));
>          if ( new_cr4 & X86_CR4_PCIDE )
>              cpu_info->pv_cr3 |= get_pcid_bits(v, true);
>          switch_cr3_cr4(v->arch.cr3, new_cr4);
> diff --git a/xen/arch/x86/pv/domain.c b/xen/arch/x86/pv/domain.c
> index 7e84b04082..2fd944b7e3 100644
> --- a/xen/arch/x86/pv/domain.c
> +++ b/xen/arch/x86/pv/domain.c
> @@ -303,7 +303,7 @@ static void _toggle_guest_pt(struct vcpu *v)
>          struct cpu_info *cpu_info = get_cpu_info();
>  
>          cpu_info->root_pgt_changed = true;
> -        cpu_info->pv_cr3 = __pa(this_cpu(root_pgt)) |
> +        cpu_info->pv_cr3 = mfn_to_maddr(this_cpu(root_pgt_mfn)) |
>                             (d->arch.pv.pcid ? get_pcid_bits(v, true)
> : 0);
>      }
>  
> diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c
> index a9a39cea6e..32dce00d10 100644
> --- a/xen/arch/x86/smpboot.c
> +++ b/xen/arch/x86/smpboot.c
> @@ -819,7 +819,7 @@ static int clone_mapping(const void *ptr,
> root_pgentry_t *rpt)
>      return rc;
>  }
>  
> -DEFINE_PER_CPU(root_pgentry_t *, root_pgt);
> +DEFINE_PER_CPU(mfn_t, root_pgt_mfn);
>  
>  static root_pgentry_t common_pgt;
>  
> @@ -827,19 +827,27 @@ extern const char _stextentry[], _etextentry[];
>  
>  static int setup_cpu_root_pgt(unsigned int cpu)
>  {
> -    root_pgentry_t *rpt;
> +    root_pgentry_t *rpt = NULL;
> +    mfn_t rpt_mfn;
>      unsigned int off;
>      int rc;
>  
>      if ( !opt_xpti_hwdom && !opt_xpti_domu )
> -        return 0;
> +    {
> +        rc = 0;
> +        goto out;
> +    }
>  
> -    rpt = alloc_xen_pagetable();
> -    if ( !rpt )
> -        return -ENOMEM;
> +    rpt_mfn = alloc_xen_pagetable_new();
> +    if ( mfn_eq(rpt_mfn, INVALID_MFN) )
> +    {
> +        rc = -ENOMEM;
> +        goto out;
> +    }
>  
> +    rpt = map_xen_pagetable_new(rpt_mfn);
>      clear_page(rpt);
> -    per_cpu(root_pgt, cpu) = rpt;
> +    per_cpu(root_pgt_mfn, cpu) = rpt_mfn;
>  
>      rpt[root_table_offset(RO_MPT_VIRT_START)] =
>          idle_pg_table[root_table_offset(RO_MPT_VIRT_START)];
> @@ -856,7 +864,7 @@ static int setup_cpu_root_pgt(unsigned int cpu)
>              rc = clone_mapping(ptr, rpt);
>  
>          if ( rc )
> -            return rc;
> +            goto out;
>  
>          common_pgt = rpt[root_table_offset(XEN_VIRT_START)];
>      }
> @@ -875,19 +883,24 @@ static int setup_cpu_root_pgt(unsigned int cpu)
>      if ( !rc )
>          rc = clone_mapping((void *)per_cpu(stubs.addr, cpu), rpt);
>  
> + out:
> +    UNMAP_XEN_PAGETABLE_NEW(rpt);
>      return rc;
>  }
>  
>  static void cleanup_cpu_root_pgt(unsigned int cpu)
>  {
> -    root_pgentry_t *rpt = per_cpu(root_pgt, cpu);
> +    mfn_t rpt_mfn = per_cpu(root_pgt_mfn, cpu);
> +    root_pgentry_t *rpt;
>      unsigned int r;
>      unsigned long stub_linear = per_cpu(stubs.addr, cpu);
>  
> -    if ( !rpt )
> +    if ( mfn_eq(rpt_mfn, INVALID_MFN) )
>          return;
>  
> -    per_cpu(root_pgt, cpu) = NULL;
> +    per_cpu(root_pgt_mfn, cpu) = INVALID_MFN;
> +
> +    rpt = map_xen_pagetable_new(rpt_mfn);
>  
>      for ( r = root_table_offset(DIRECTMAP_VIRT_START);
>            r < root_table_offset(HYPERVISOR_VIRT_END); ++r )
> @@ -932,7 +945,8 @@ static void cleanup_cpu_root_pgt(unsigned int
> cpu)
>          free_xen_pagetable_new(l3t_mfn);
>      }
>  
> -    free_xen_pagetable(rpt);
> +    UNMAP_XEN_PAGETABLE_NEW(rpt);
> +    free_xen_pagetable_new(rpt_mfn);
>  
>      /* Also zap the stub mapping for this CPU. */
>      if ( stub_linear )
> @@ -1138,7 +1152,7 @@ void __init smp_prepare_cpus(void)
>      rc = setup_cpu_root_pgt(0);
>      if ( rc )
>          panic("Error %d setting up PV root page table\n", rc);
> -    if ( per_cpu(root_pgt, 0) )
> +    if ( !mfn_eq(per_cpu(root_pgt_mfn, 0), INVALID_MFN) )
>      {
>          get_cpu_info()->pv_cr3 = 0;
>  
> diff --git a/xen/include/asm-x86/mm.h b/xen/include/asm-x86/mm.h
> index 4378d9f815..708b84bb89 100644
> --- a/xen/include/asm-x86/mm.h
> +++ b/xen/include/asm-x86/mm.h
> @@ -657,4 +657,6 @@ void free_xen_pagetable_new(mfn_t mfn);
>  
>  l1_pgentry_t *virt_to_xen_l1e(unsigned long v);
>  
> +DECLARE_PER_CPU(mfn_t, root_pgt_mfn);
> +
>  #endif /* __ASM_X86_MM_H__ */
> diff --git a/xen/include/asm-x86/processor.h b/xen/include/asm-
> x86/processor.h
> index df01ae30d7..9f98ac96f5 100644
> --- a/xen/include/asm-x86/processor.h
> +++ b/xen/include/asm-x86/processor.h
> @@ -449,7 +449,6 @@ extern idt_entry_t idt_table[];
>  extern idt_entry_t *idt_tables[];
>  
>  DECLARE_PER_CPU(struct tss_struct, init_tss);
> -DECLARE_PER_CPU(root_pgentry_t *, root_pgt);
>  
>  extern void write_ptbase(struct vcpu *v);
>  



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