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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH RFC] xen/mapcache: store dma information in revmapcache entries for debugging
On 03/05/2017 02:08, Stefano Stabellini wrote:
> The Xen mapcache is able to create long term mappings, they are called
> "locked" mappings. The third parameter of the xen_map_cache call
> specifies if a mapping is a "locked" mapping.
>
>
> From the QEMU point of view there are two kinds of long term mappings:
>
> [a] device memory mappings, such as option roms and video memory
> [b] dma mappings, created by dma_memory_map & friends
>
> After certain operations, ballooning a VM in particular, Xen asks QEMU
> kindly to destroy all mappings. However, certainly [a] mappings are
> present and cannot be removed. That's not a problem as they are not
> affected by balloonning. The *real* problem is that if there are any
> mappings of type [b], any outstanding dma operations could fail. This is
> a known shortcoming. In other words, when Xen asks QEMU to destroy all
> mappings, it is an error if any [b] mappings exist.
>
> However today we have no way of distinguishing [a] from [b]. Because of
> that, we cannot even print a decent warning.
>
> This patch introduces a new "dma" bool field to MapCacheRev entires, to
> remember if a given mapping is for dma or is a long term device memory
> mapping. When xen_invalidate_map_cache is called, we print a warning if
> any [b] mappings exist. We ignore [a] mappings.
>
> Mappings created by qemu_map_ram_ptr are assumed to be [a], while
> mappings created by address_space_map->qemu_ram_ptr_length are assumed
> to be [b].
>
> The goal of the patch is to make debugging and system understanding
> easier.
Sure, why not.
Acked-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Paolo
> Signed-off-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
>
> diff --git a/exec.c b/exec.c
> index eac6085..85769e1 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2084,10 +2084,10 @@ void *qemu_map_ram_ptr(RAMBlock *ram_block,
> ram_addr_t addr)
> * In that case just map until the end of the page.
> */
> if (block->offset == 0) {
> - return xen_map_cache(addr, 0, 0);
> + return xen_map_cache(addr, 0, 0, false);
> }
>
> - block->host = xen_map_cache(block->offset, block->max_length, 1);
> + block->host = xen_map_cache(block->offset, block->max_length, 1,
> false);
> }
> return ramblock_ptr(block, addr);
> }
> @@ -2117,10 +2117,10 @@ static void *qemu_ram_ptr_length(RAMBlock *ram_block,
> ram_addr_t addr,
> * In that case just map the requested area.
> */
> if (block->offset == 0) {
> - return xen_map_cache(addr, *size, 1);
> + return xen_map_cache(addr, *size, 1, true);
> }
>
> - block->host = xen_map_cache(block->offset, block->max_length, 1);
> + block->host = xen_map_cache(block->offset, block->max_length, 1,
> true);
> }
>
> return ramblock_ptr(block, addr);
> diff --git a/hw/i386/xen/xen-mapcache.c b/hw/i386/xen/xen-mapcache.c
> index 31debdf..fa4282a 100644
> --- a/hw/i386/xen/xen-mapcache.c
> +++ b/hw/i386/xen/xen-mapcache.c
> @@ -62,6 +62,7 @@ typedef struct MapCacheRev {
> hwaddr paddr_index;
> hwaddr size;
> QTAILQ_ENTRY(MapCacheRev) next;
> + bool dma;
> } MapCacheRev;
>
> typedef struct MapCache {
> @@ -202,7 +203,7 @@ static void xen_remap_bucket(MapCacheEntry *entry,
> }
>
> static uint8_t *xen_map_cache_unlocked(hwaddr phys_addr, hwaddr size,
> - uint8_t lock)
> + uint8_t lock, bool dma)
> {
> MapCacheEntry *entry, *pentry = NULL;
> hwaddr address_index;
> @@ -289,6 +290,7 @@ tryagain:
> if (lock) {
> MapCacheRev *reventry = g_malloc0(sizeof(MapCacheRev));
> entry->lock++;
> + reventry->dma = dma;
> reventry->vaddr_req = mapcache->last_entry->vaddr_base +
> address_offset;
> reventry->paddr_index = mapcache->last_entry->paddr_index;
> reventry->size = entry->size;
> @@ -300,12 +302,12 @@ tryagain:
> }
>
> uint8_t *xen_map_cache(hwaddr phys_addr, hwaddr size,
> - uint8_t lock)
> + uint8_t lock, bool dma)
> {
> uint8_t *p;
>
> mapcache_lock();
> - p = xen_map_cache_unlocked(phys_addr, size, lock);
> + p = xen_map_cache_unlocked(phys_addr, size, lock, dma);
> mapcache_unlock();
> return p;
> }
> @@ -426,8 +428,10 @@ void xen_invalidate_map_cache(void)
> 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",
> + if (!reventry->dma)
> + continue;
> + fprintf(stderr, "Locked DMA mapping while invalidating mapcache!"
> + " "TARGET_FMT_plx" -> %p is present\n",
> reventry->paddr_index, reventry->vaddr_req);
> }
>
> diff --git a/include/sysemu/xen-mapcache.h b/include/sysemu/xen-mapcache.h
> index b8c93b9..01daaad 100644
> --- a/include/sysemu/xen-mapcache.h
> +++ b/include/sysemu/xen-mapcache.h
> @@ -17,7 +17,7 @@ typedef hwaddr (*phys_offset_to_gaddr_t)(hwaddr start_addr,
> void xen_map_cache_init(phys_offset_to_gaddr_t f,
> void *opaque);
> uint8_t *xen_map_cache(hwaddr phys_addr, hwaddr size,
> - uint8_t lock);
> + uint8_t lock, bool dma);
> 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);
> @@ -31,7 +31,8 @@ static inline void
> xen_map_cache_init(phys_offset_to_gaddr_t f,
>
> static inline uint8_t *xen_map_cache(hwaddr phys_addr,
> hwaddr size,
> - uint8_t lock)
> + uint8_t lock,
> + bool dma)
> {
> abort();
> }
>
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