Re: [Xen-devel] [PATCH v2 3/4] xen/mapcache: introduce xen_replace_cache_entry()

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Igor Druzhinin
> Sent: 04 July 2017 17:34
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx;
> qemu-devel@xxxxxxxxxx
> Cc: sstabellini@xxxxxxxxxx; Anthony Perard <anthony.perard@xxxxxxxxxx>;
> pbonzini@xxxxxxxxxx
> Subject: Re: [PATCH v2 3/4] xen/mapcache: introduce
> xen_replace_cache_entry()
> 
> On 04/07/17 17:27, Paul Durrant wrote:
> >> -----Original Message-----
> >> From: Igor Druzhinin
> >> Sent: 04 July 2017 16:48
> >> To: xen-devel@xxxxxxxxxxxxxxxxxxxx; qemu-devel@xxxxxxxxxx
> >> Cc: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>; sstabellini@xxxxxxxxxx;
> >> Anthony Perard <anthony.perard@xxxxxxxxxx>; Paul Durrant
> >> <Paul.Durrant@xxxxxxxxxx>; pbonzini@xxxxxxxxxx
> >> Subject: [PATCH v2 3/4] xen/mapcache: introduce
> >> xen_replace_cache_entry()
> >>
> >> This new call is trying to update a requested map cache entry
> >> according to the changes in the physmap. The call is searching
> >> for the entry, unmaps it and maps again at the same place using
> >> a new guest address. If the mapping is dummy this call will
> >> make it real.
> >>
> >> This function makes use of a new xenforeignmemory_map2() call
> >> with an extended interface that was recently introduced in
> >> libxenforeignmemory [1].
> >
> > I don't understand how the compat layer works here. If
> xenforeignmemory_map2() is not available then you can't control the
> placement in virtual address space.
> >
> 
> If it's not 4.10 or newer xenforeignmemory_map2() doesn't exist and is
> going to be defined as xenforeignmemory_map(). At the same time
> XEN_COMPAT_PHYSMAP is defined and the entry replace function (which
> relies on xenforeignmemory_map2 functionality) is never going to be called.
> 
> If you mean that I should incorporate this into the description I can do it.

AFAICT XEN_COMPAT_PHYSMAP is not introduced until patch #4 though.

The problem really comes down to defining xenforeignmemory_map2() in terms of 
xenforeignmemory_map(). It basically can't be safely done. Could you define 
xenforeignmemory_map2() as abort() in the compat case instead? 

  Paul

> 
> Igor
> 
> >   Paul
> >
> >>
> >> [1] https://www.mail-archive.com/xen-
> devel@xxxxxxxxxxxxx/msg113007.html
> >>
> >> Signed-off-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
> >> ---
> >>  configure                     | 18 ++++++++++
> >>  hw/i386/xen/xen-mapcache.c    | 79
> >> ++++++++++++++++++++++++++++++++++++++-----
> >>  include/hw/xen/xen_common.h   |  7 ++++
> >>  include/sysemu/xen-mapcache.h | 11 +++++-
> >>  4 files changed, 106 insertions(+), 9 deletions(-)
> >>
> >> diff --git a/configure b/configure
> >> index c571ad1..ad6156b 100755
> >> --- a/configure
> >> +++ b/configure
> >> @@ -2021,6 +2021,24 @@ EOF
> >>      # Xen unstable
> >>      elif
> >>          cat > $TMPC <<EOF &&
> >> +#undef XC_WANT_COMPAT_MAP_FOREIGN_API
> >> +#include <xenforeignmemory.h>
> >> +int main(void) {
> >> +  xenforeignmemory_handle *xfmem;
> >> +
> >> +  xfmem = xenforeignmemory_open(0, 0);
> >> +  xenforeignmemory_map2(xfmem, 0, 0, 0, 0, 0, 0, 0);
> >> +
> >> +  return 0;
> >> +}
> >> +EOF
> >> +        compile_prog "" "$xen_libs -lxendevicemodel $xen_stable_libs"
> >> +      then
> >> +      xen_stable_libs="-lxendevicemodel $xen_stable_libs"
> >> +      xen_ctrl_version=41000
> >> +      xen=yes
> >> +    elif
> >> +        cat > $TMPC <<EOF &&
> >>  #undef XC_WANT_COMPAT_DEVICEMODEL_API
> >>  #define __XEN_TOOLS__
> >>  #include <xendevicemodel.h>
> >> diff --git a/hw/i386/xen/xen-mapcache.c b/hw/i386/xen/xen-mapcache.c
> >> index cd4e746..a988be7 100644
> >> --- a/hw/i386/xen/xen-mapcache.c
> >> +++ b/hw/i386/xen/xen-mapcache.c
> >> @@ -151,6 +151,7 @@ void
> xen_map_cache_init(phys_offset_to_gaddr_t f,
> >> void *opaque)
> >>  }
> >>
> >>  static void xen_remap_bucket(MapCacheEntry *entry,
> >> +                             void *vaddr,
> >>                               hwaddr size,
> >>                               hwaddr address_index,
> >>                               bool dummy)
> >> @@ -167,7 +168,9 @@ static void xen_remap_bucket(MapCacheEntry
> >> *entry,
> >>      err = g_malloc0(nb_pfn * sizeof (int));
> >>
> >>      if (entry->vaddr_base != NULL) {
> >> -        ram_block_notify_remove(entry->vaddr_base, entry->size);
> >> +        if (entry->vaddr_base != vaddr) {
> >> +            ram_block_notify_remove(entry->vaddr_base, entry->size);
> >> +        }
> >>          if (munmap(entry->vaddr_base, entry->size) != 0) {
> >>              perror("unmap fails");
> >>              exit(-1);
> >> @@ -181,11 +184,11 @@ static void xen_remap_bucket(MapCacheEntry
> >> *entry,
> >>      }
> >>
> >>      if (!dummy) {
> >> -        vaddr_base = xenforeignmemory_map(xen_fmem, xen_domid,
> >> -                                           PROT_READ|PROT_WRITE,
> >> +        vaddr_base = xenforeignmemory_map2(xen_fmem, xen_domid,
> >> vaddr,
> >> +                                           PROT_READ|PROT_WRITE, 0,
> >>                                             nb_pfn, pfns, err);
> >>          if (vaddr_base == NULL) {
> >> -            perror("xenforeignmemory_map");
> >> +            perror("xenforeignmemory_map2");
> >>              exit(-1);
> >>          }
> >>          entry->flags &= ~(XEN_MAPCACHE_ENTRY_DUMMY);
> >> @@ -194,7 +197,7 @@ static void xen_remap_bucket(MapCacheEntry
> >> *entry,
> >>           * We create dummy mappings where we are unable to create a
> foreign
> >>           * mapping immediately due to certain circumstances (i.e. on 
> >> resume
> >> now)
> >>           */
> >> -        vaddr_base = mmap(NULL, size, PROT_READ|PROT_WRITE,
> >> +        vaddr_base = mmap(vaddr, size, PROT_READ|PROT_WRITE,
> >>                            MAP_ANON|MAP_SHARED, -1, 0);
> >>          if (vaddr_base == NULL) {
> >>              perror("mmap");
> >> @@ -203,13 +206,16 @@ static void xen_remap_bucket(MapCacheEntry
> >> *entry,
> >>          entry->flags |= XEN_MAPCACHE_ENTRY_DUMMY;
> >>      }
> >>
> >> +    if (entry->vaddr_base == NULL || entry->vaddr_base != vaddr) {
> >> +        ram_block_notify_add(vaddr_base, size);
> >> +    }
> >> +
> >>      entry->vaddr_base = vaddr_base;
> >>      entry->paddr_index = address_index;
> >>      entry->size = size;
> >>      entry->valid_mapping = (unsigned long *) g_malloc0(sizeof(unsigned
> long)
> >> *
> >>              BITS_TO_LONGS(size >> XC_PAGE_SHIFT));
> >>
> >> -    ram_block_notify_add(entry->vaddr_base, entry->size);
> >>      bitmap_zero(entry->valid_mapping, nb_pfn);
> >>      for (i = 0; i < nb_pfn; i++) {
> >>          if (!err[i]) {
> >> @@ -282,14 +288,14 @@ tryagain:
> >>      if (!entry) {
> >>          entry = g_malloc0(sizeof (MapCacheEntry));
> >>          pentry->next = entry;
> >> -        xen_remap_bucket(entry, cache_size, address_index, dummy);
> >> +        xen_remap_bucket(entry, NULL, cache_size, address_index,
> dummy);
> >>      } else if (!entry->lock) {
> >>          if (!entry->vaddr_base || entry->paddr_index != address_index ||
> >>                  entry->size != cache_size ||
> >>                  !test_bits(address_offset >> XC_PAGE_SHIFT,
> >>                      test_bit_size >> XC_PAGE_SHIFT,
> >>                      entry->valid_mapping)) {
> >> -            xen_remap_bucket(entry, cache_size, address_index, dummy);
> >> +            xen_remap_bucket(entry, NULL, cache_size, address_index,
> >> dummy);
> >>          }
> >>      }
> >>
> >> @@ -486,3 +492,60 @@ void xen_invalidate_map_cache(void)
> >>
> >>      mapcache_unlock();
> >>  }
> >> +
> >> +static uint8_t *xen_replace_cache_entry_unlocked(hwaddr
> >> old_phys_addr,
> >> +                                                 hwaddr new_phys_addr,
> >> +                                                 hwaddr size)
> >> +{
> >> +    MapCacheEntry *entry;
> >> +    hwaddr address_index;
> >> +    hwaddr address_offset;
> >> +    hwaddr cache_size = size;
> >> +    hwaddr test_bit_size;
> >> +
> >> +    address_index  = old_phys_addr >> MCACHE_BUCKET_SHIFT;
> >> +    address_offset = old_phys_addr & (MCACHE_BUCKET_SIZE - 1);
> >> +
> >> +    assert(size);
> >> +    /* test_bit_size is always a multiple of XC_PAGE_SIZE */
> >> +    test_bit_size = size + (old_phys_addr & (XC_PAGE_SIZE - 1));
> >> +    if (test_bit_size % XC_PAGE_SIZE) {
> >> +        test_bit_size += XC_PAGE_SIZE - (test_bit_size % XC_PAGE_SIZE);
> >> +    }
> >> +    cache_size = size + address_offset;
> >> +    if (cache_size % MCACHE_BUCKET_SIZE) {
> >> +        cache_size += MCACHE_BUCKET_SIZE - (cache_size %
> >> MCACHE_BUCKET_SIZE);
> >> +    }
> >> +
> >> +    entry = &mapcache->entry[address_index % mapcache->nr_buckets];
> >> +    while (entry && !(entry->paddr_index == address_index && entry-
> >size
> >> == cache_size)) {
> >> +        entry = entry->next;
> >> +    }
> >> +    if (!entry) {
> >> +        DPRINTF("Trying to update an entry for %lx that is not in the
> >> mapcache!\n", phys_addr);
> >> +        return NULL;
> >> +    }
> >> +
> >> +    address_index  = new_phys_addr >> MCACHE_BUCKET_SHIFT;
> >> +    address_offset = new_phys_addr & (MCACHE_BUCKET_SIZE - 1);
> >> +
> >> +    xen_remap_bucket(entry, entry->vaddr_base, cache_size,
> >> address_index, false);
> >> +    if(!test_bits(address_offset >> XC_PAGE_SHIFT,
> >> +                test_bit_size >> XC_PAGE_SHIFT,
> >> +                entry->valid_mapping)) {
> >> +        DPRINTF("Unable to update an entry for %lx in the mapcache!\n",
> >> phys_addr);
> >> +        return NULL;
> >> +    }
> >> +
> >> +    return entry->vaddr_base + address_offset;
> >> +}
> >> +
> >> +uint8_t *xen_replace_cache_entry(hwaddr old_phys_addr, hwaddr
> >> new_phys_addr, hwaddr size)
> >> +{
> >> +    uint8_t *p;
> >> +
> >> +    mapcache_lock();
> >> +    p = xen_replace_cache_entry_unlocked(old_phys_addr,
> >> new_phys_addr, size);
> >> +    mapcache_unlock();
> >> +    return p;
> >> +}
> >> diff --git a/include/hw/xen/xen_common.h
> >> b/include/hw/xen/xen_common.h
> >> index e00ddd7..70a5cad 100644
> >> --- a/include/hw/xen/xen_common.h
> >> +++ b/include/hw/xen/xen_common.h
> >> @@ -78,6 +78,13 @@ static inline void
> >> *xenforeignmemory_map(xc_interface *h, uint32_t dom,
> >>
> >>  extern xenforeignmemory_handle *xen_fmem;
> >>
> >> +#if CONFIG_XEN_CTRL_INTERFACE_VERSION < 41000
> >> +
> >> +#define xenforeignmemory_map2(h, d, a, p, f, ps, ar, e) \
> >> +    xenforeignmemory_map(h, d, p, ps, ar, e)
> >> +
> >> +#endif
> >> +
> >>  #if CONFIG_XEN_CTRL_INTERFACE_VERSION < 40900
> >>
> >>  typedef xc_interface xendevicemodel_handle;
> >> diff --git a/include/sysemu/xen-mapcache.h b/include/sysemu/xen-
> >> mapcache.h
> >> index 01daaad..b38962c 100644
> >> --- a/include/sysemu/xen-mapcache.h
> >> +++ b/include/sysemu/xen-mapcache.h
> >> @@ -21,7 +21,9 @@ uint8_t *xen_map_cache(hwaddr phys_addr,
> hwaddr
> >> size,
> >>  ram_addr_t xen_ram_addr_from_mapcache(void *ptr);
> >>  void xen_invalidate_map_cache_entry(uint8_t *buffer);
> >>  void xen_invalidate_map_cache(void);
> >> -
> >> +uint8_t *xen_replace_cache_entry(hwaddr old_phys_addr,
> >> +                                 hwaddr new_phys_addr,
> >> +                                 hwaddr size);
> >>  #else
> >>
> >>  static inline void xen_map_cache_init(phys_offset_to_gaddr_t f,
> >> @@ -50,6 +52,13 @@ static inline void xen_invalidate_map_cache(void)
> >>  {
> >>  }
> >>
> >> +uint8_t *xen_replace_cache_entry(hwaddr old_phys_addr,
> >> +                                 hwaddr new_phys_addr,
> >> +                                 hwaddr size)
> >> +{
> >> +    abort();
> >> +}
> >> +
> >>  #endif
> >>
> >>  #endif /* XEN_MAPCACHE_H */
> >> --
> >> 2.7.4
> >
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