Re: [PATCH v2 2/4] x86/mm: use optional cache in guest_walk_tables()

[Paul Durrant <Paul.Durrant@citrix.com>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@suse.com]
> Sent: 11 September 2018 14:15
> To: xen-devel <xen-devel@lists.xenproject.org>
> Cc: Andrew Cooper <Andrew.Cooper3@citrix.com>; Paul Durrant
> <Paul.Durrant@citrix.com>; Wei Liu <wei.liu2@citrix.com>; George Dunlap
> <George.Dunlap@citrix.com>
> Subject: [PATCH v2 2/4] x86/mm: use optional cache in guest_walk_tables()
> 
> The caching isn't actually implemented here, this is just setting the
> stage.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> ---
> v2: Don't wrongly use top_gfn for non-root gpa calculation. Re-write
>     cache entries after setting A/D bits (an alternative would be to
>     suppress their setting upon cache hits).
> 
> --- a/xen/arch/x86/hvm/emulate.c
> +++ b/xen/arch/x86/hvm/emulate.c
> @@ -2664,6 +2664,18 @@ void hvm_dump_emulation_state(const char
>             hvmemul_ctxt->insn_buf);
>  }
> 
> +bool hvmemul_read_cache(const struct hvmemul_cache *cache, paddr_t
> gpa,
> +                        unsigned int level, void *buffer, unsigned int size)
> +{
> +    return false;
> +}
> +
> +void hvmemul_write_cache(struct hvmemul_cache *cache, paddr_t gpa,
> +                         unsigned int level, const void *buffer,
> +                         unsigned int size)
> +{
> +}
> +
>  /*
>   * Local variables:
>   * mode: C
> --- a/xen/arch/x86/mm/guest_walk.c
> +++ b/xen/arch/x86/mm/guest_walk.c
> @@ -92,8 +92,13 @@ guest_walk_tables(struct vcpu *v, struct
>  #if GUEST_PAGING_LEVELS >= 4 /* 64-bit only... */
>      guest_l3e_t *l3p = NULL;

Shouldn't the above line be...

>      guest_l4e_t *l4p;
> +    paddr_t l4gpa;
> +#endif
> +#if GUEST_PAGING_LEVELS >= 3 /* PAE or 64... */

...here?

> +    paddr_t l3gpa;
>  #endif
>      uint32_t gflags, rc;
> +    paddr_t l1gpa = 0, l2gpa = 0;
>      unsigned int leaf_level;
>      p2m_query_t qt = P2M_ALLOC | P2M_UNSHARE;
> 
> @@ -134,7 +139,15 @@ guest_walk_tables(struct vcpu *v, struct
>      /* Get the l4e from the top level table and check its flags*/
>      gw->l4mfn = top_mfn;
>      l4p = (guest_l4e_t *) top_map;
> -    gw->l4e = l4p[guest_l4_table_offset(gla)];
> +    l4gpa = gfn_to_gaddr(top_gfn) +
> +            guest_l4_table_offset(gla) * sizeof(gw->l4e);
> +    if ( !cache ||
> +         !hvmemul_read_cache(cache, l4gpa, 4, &gw->l4e, sizeof(gw->l4e)) )
> +    {
> +        gw->l4e = l4p[guest_l4_table_offset(gla)];
> +        if ( cache )
> +            hvmemul_write_cache(cache, l4gpa, 4, &gw->l4e, sizeof(gw->l4e));

No need to test cache here or below since neither the read or write functions (yet) dereference it.

  Paul

> +    }
>      gflags = guest_l4e_get_flags(gw->l4e);
>      if ( !(gflags & _PAGE_PRESENT) )
>          goto out;
> @@ -164,7 +177,15 @@ guest_walk_tables(struct vcpu *v, struct
>      }
> 
>      /* Get the l3e and check its flags*/
> -    gw->l3e = l3p[guest_l3_table_offset(gla)];
> +    l3gpa = gfn_to_gaddr(guest_l4e_get_gfn(gw->l4e)) +
> +            guest_l3_table_offset(gla) * sizeof(gw->l3e);
> +    if ( !cache ||
> +         !hvmemul_read_cache(cache, l3gpa, 3, &gw->l3e, sizeof(gw->l3e)) )
> +    {
> +        gw->l3e = l3p[guest_l3_table_offset(gla)];
> +        if ( cache )
> +            hvmemul_write_cache(cache, l3gpa, 3, &gw->l3e, sizeof(gw->l3e));
> +    }
>      gflags = guest_l3e_get_flags(gw->l3e);
>      if ( !(gflags & _PAGE_PRESENT) )
>          goto out;
> @@ -216,7 +237,16 @@ guest_walk_tables(struct vcpu *v, struct
>  #else /* PAE only... */
> 
>      /* Get the l3e and check its flag */
> -    gw->l3e = ((guest_l3e_t *)top_map)[guest_l3_table_offset(gla)];
> +    l3gpa = gfn_to_gaddr(top_gfn) + ((unsigned long)top_map &
> ~PAGE_MASK) +
> +            guest_l3_table_offset(gla) * sizeof(gw->l3e);
> +    if ( !cache ||
> +         !hvmemul_read_cache(cache, l3gpa, 3, &gw->l3e, sizeof(gw->l3e)) )
> +    {
> +        gw->l3e = ((guest_l3e_t *)top_map)[guest_l3_table_offset(gla)];
> +        if ( cache )
> +            hvmemul_write_cache(cache, l3gpa, 3, &gw->l3e, sizeof(gw->l3e));
> +    }
> +
>      gflags = guest_l3e_get_flags(gw->l3e);
>      if ( !(gflags & _PAGE_PRESENT) )
>          goto out;
> @@ -242,18 +272,26 @@ guest_walk_tables(struct vcpu *v, struct
>          goto out;
>      }
> 
> -    /* Get the l2e */
> -    gw->l2e = l2p[guest_l2_table_offset(gla)];
> +    l2gpa = gfn_to_gaddr(guest_l3e_get_gfn(gw->l3e));
> 
>  #else /* 32-bit only... */
> 
> -    /* Get l2e from the top level table */
>      gw->l2mfn = top_mfn;
>      l2p = (guest_l2e_t *) top_map;
> -    gw->l2e = l2p[guest_l2_table_offset(gla)];
> +    l2gpa = gfn_to_gaddr(top_gfn);
> 
>  #endif /* All levels... */
> 
> +    /* Get the l2e */
> +    l2gpa += guest_l2_table_offset(gla) * sizeof(gw->l2e);
> +    if ( !cache ||
> +         !hvmemul_read_cache(cache, l2gpa, 2, &gw->l2e, sizeof(gw->l2e)) )
> +    {
> +        gw->l2e = l2p[guest_l2_table_offset(gla)];
> +        if ( cache )
> +            hvmemul_write_cache(cache, l2gpa, 2, &gw->l2e, sizeof(gw->l2e));
> +    }
> +
>      /* Check the l2e flags. */
>      gflags = guest_l2e_get_flags(gw->l2e);
>      if ( !(gflags & _PAGE_PRESENT) )
> @@ -335,7 +373,17 @@ guest_walk_tables(struct vcpu *v, struct
>          gw->pfec |= rc & PFEC_synth_mask;
>          goto out;
>      }
> -    gw->l1e = l1p[guest_l1_table_offset(gla)];
> +
> +    l1gpa = gfn_to_gaddr(guest_l2e_get_gfn(gw->l2e)) +
> +            guest_l1_table_offset(gla) * sizeof(gw->l1e);
> +    if ( !cache ||
> +         !hvmemul_read_cache(cache, l1gpa, 1, &gw->l1e, sizeof(gw->l1e)) )
> +    {
> +        gw->l1e = l1p[guest_l1_table_offset(gla)];
> +        if ( cache )
> +            hvmemul_write_cache(cache, l1gpa, 1, &gw->l1e, sizeof(gw->l1e));
> +    }
> +
>      gflags = guest_l1e_get_flags(gw->l1e);
>      if ( !(gflags & _PAGE_PRESENT) )
>          goto out;
> @@ -446,22 +494,38 @@ guest_walk_tables(struct vcpu *v, struct
>      case 1:
>          if ( set_ad_bits(&l1p[guest_l1_table_offset(gla)].l1, &gw->l1e.l1,
>                           (walk & PFEC_write_access)) )
> +        {
>              paging_mark_dirty(d, gw->l1mfn);
> +            if ( cache )
> +                hvmemul_write_cache(cache, l1gpa, 1, &gw->l1e, sizeof(gw->l1e));
> +        }
>          /* Fallthrough */
>      case 2:
>          if ( set_ad_bits(&l2p[guest_l2_table_offset(gla)].l2, &gw->l2e.l2,
>                           (walk & PFEC_write_access) && leaf_level == 2) )
> +        {
>              paging_mark_dirty(d, gw->l2mfn);
> +            if ( cache )
> +                hvmemul_write_cache(cache, l2gpa, 2, &gw->l2e, sizeof(gw->l2e));
> +        }
>          /* Fallthrough */
>  #if GUEST_PAGING_LEVELS == 4 /* 64-bit only... */
>      case 3:
>          if ( set_ad_bits(&l3p[guest_l3_table_offset(gla)].l3, &gw->l3e.l3,
>                           (walk & PFEC_write_access) && leaf_level == 3) )
> +        {
>              paging_mark_dirty(d, gw->l3mfn);
> +            if ( cache )
> +                hvmemul_write_cache(cache, l3gpa, 3, &gw->l3e, sizeof(gw->l3e));
> +        }
> 
>          if ( set_ad_bits(&l4p[guest_l4_table_offset(gla)].l4, &gw->l4e.l4,
>                           false) )
> +        {
>              paging_mark_dirty(d, gw->l4mfn);
> +            if ( cache )
> +                hvmemul_write_cache(cache, l4gpa, 4, &gw->l4e, sizeof(gw->l4e));
> +        }
>  #endif
>      }
> 
> --- a/xen/include/asm-x86/hvm/emulate.h
> +++ b/xen/include/asm-x86/hvm/emulate.h
> @@ -98,6 +98,13 @@ int hvmemul_do_pio_buffer(uint16_t port,
>                            uint8_t dir,
>                            void *buffer);
> 
> +struct hvmemul_cache;
> +bool hvmemul_read_cache(const struct hvmemul_cache *, paddr_t gpa,
> +                        unsigned int level, void *buffer, unsigned int size);
> +void hvmemul_write_cache(struct hvmemul_cache *, paddr_t gpa,
> +                         unsigned int level, const void *buffer,
> +                         unsigned int size);
> +
>  void hvm_dump_emulation_state(const char *loglvl, const char *prefix,
>                                struct hvm_emulate_ctxt *hvmemul_ctxt, int rc);
> 
> 
> 


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