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Re: [Qemu-devel] [RFH PATCH 2/2] xen: add a lock for the mapcache


From: Stefano Stabellini
Subject: Re: [Qemu-devel] [RFH PATCH 2/2] xen: add a lock for the mapcache
Date: Wed, 14 Jan 2015 11:52:36 +0000
User-agent: Alpine 2.02 (DEB 1266 2009-07-14)

On Wed, 14 Jan 2015, Paolo Bonzini wrote:
> Extend the existing dummy mapcache_lock/unlock macros to cover all of
> xen-mapcache.c.  This prepares for unlocked memory access, when parts
> of exec.c will not be protected by the BQL.
> 
> Signed-off-by: Paolo Bonzini <address@hidden>

Acked-by: Stefano Stabellini <address@hidden>


>  xen-mapcache.c | 54 +++++++++++++++++++++++++++++++++++++++++++-----------
>  1 file changed, 43 insertions(+), 11 deletions(-)
> 
> diff --git a/xen-mapcache.c b/xen-mapcache.c
> index 458069b..8cefd0c 100644
> --- a/xen-mapcache.c
> +++ b/xen-mapcache.c
> @@ -49,9 +49,6 @@
>   */
>  #define NON_MCACHE_MEMORY_SIZE (80 * 1024 * 1024)
>  
> -#define mapcache_lock()   ((void)0)
> -#define mapcache_unlock() ((void)0)
> -
>  typedef struct MapCacheEntry {
>      hwaddr paddr_index;
>      uint8_t *vaddr_base;
> @@ -79,11 +76,22 @@ typedef struct MapCache {
>      unsigned int mcache_bucket_shift;
>  
>      phys_offset_to_gaddr_t phys_offset_to_gaddr;
> +    QemuMutex lock;
>      void *opaque;
>  } MapCache;
>  
>  static MapCache *mapcache;
>  
> +static inline void mapcache_lock(void)
> +{
> +    qemu_mutex_lock(&mapcache->lock);
> +}
> +
> +static inline void mapcache_unlock(void)
> +{
> +    qemu_mutex_unlock(&mapcache->lock);
> +}
> +
>  static inline int test_bits(int nr, int size, const unsigned long *addr)
>  {
>      unsigned long res = find_next_zero_bit(addr, size + nr, nr);
> @@ -102,6 +110,7 @@ void xen_map_cache_init(phys_offset_to_gaddr_t f, void 
> *opaque)
>  
>      mapcache->phys_offset_to_gaddr = f;
>      mapcache->opaque = opaque;
> +    qemu_mutex_init(&mapcache->lock);
>  
>      QTAILQ_INIT(&mapcache->locked_entries);
>  
> @@ -193,8 +202,8 @@ static void xen_remap_bucket(MapCacheEntry *entry,
>      g_free(err);
>  }
>  
> -uint8_t *xen_map_cache(hwaddr phys_addr, hwaddr size,
> -                       uint8_t lock)
> +static uint8_t *xen_map_cache_unlocked(hwaddr phys_addr, hwaddr size,
> +                                       uint8_t lock)
>  {
>      MapCacheEntry *entry, *pentry = NULL;
>      hwaddr address_index;
> @@ -291,14 +300,27 @@ tryagain:
>      return mapcache->last_entry->vaddr_base + address_offset;
>  }
>  
> +uint8_t *xen_map_cache(hwaddr phys_addr, hwaddr size,
> +                       uint8_t lock)
> +{
> +    uint8_t *p;
> +
> +    mapcache_lock();
> +    p = xen_map_cache_unlocked(phys_addr, size, lock);
> +    mapcache_unlock();
> +    return p;
> +}
> +
>  ram_addr_t xen_ram_addr_from_mapcache(void *ptr)
>  {
>      MapCacheEntry *entry = NULL;
>      MapCacheRev *reventry;
>      hwaddr paddr_index;
>      hwaddr size;
> +    ram_addr_t raddr;
>      int found = 0;
>  
> +    mapcache_lock();
>      QTAILQ_FOREACH(reventry, &mapcache->locked_entries, next) {
>          if (reventry->vaddr_req == ptr) {
>              paddr_index = reventry->paddr_index;
> @@ -323,13 +345,16 @@ ram_addr_t xen_ram_addr_from_mapcache(void *ptr)
>      }
>      if (!entry) {
>          DPRINTF("Trying to find address %p that is not in the mapcache!\n", 
> ptr);
> -        return 0;
> +        raddr = 0;
> +    } else {
> +        raddr = (reventry->paddr_index << MCACHE_BUCKET_SHIFT) +
> +             ((unsigned long) ptr - (unsigned long) entry->vaddr_base);
>      }
> -    return (reventry->paddr_index << MCACHE_BUCKET_SHIFT) +
> -        ((unsigned long) ptr - (unsigned long) entry->vaddr_base);
> +    mapcache_unlock();
> +    return raddr;
>  }
>  
> -void xen_invalidate_map_cache_entry(uint8_t *buffer)
> +static void xen_invalidate_map_cache_entry_unlocked(uint8_t *buffer)
>  {
>      MapCacheEntry *entry = NULL, *pentry = NULL;
>      MapCacheRev *reventry;
> @@ -383,6 +408,13 @@ void xen_invalidate_map_cache_entry(uint8_t *buffer)
>      g_free(entry);
>  }
>  
> +void xen_invalidate_map_cache_entry(uint8_t *buffer)
> +{
> +    mapcache_lock();
> +    xen_invalidate_map_cache_entry_unlocked(buffer);
> +    mapcache_unlock();
> +}
> +
>  void xen_invalidate_map_cache(void)
>  {
>      unsigned long i;
> @@ -391,14 +423,14 @@ void xen_invalidate_map_cache(void)
>      /* Flush pending AIO before destroying the mapcache */
>      bdrv_drain_all();
>  
> +    mapcache_lock();
> +
>      QTAILQ_FOREACH(reventry, &mapcache->locked_entries, next) {
>          DPRINTF("There should be no locked mappings at this time, "
>                  "but "TARGET_FMT_plx" -> %p is present\n",
>                  reventry->paddr_index, reventry->vaddr_req);
>      }
>  
> -    mapcache_lock();
> -
>      for (i = 0; i < mapcache->nr_buckets; i++) {
>          MapCacheEntry *entry = &mapcache->entry[i];
>  
> -- 
> 1.8.3.1
> 



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