Commit 1ff7c598 authored by Stefano Stabellini's avatar Stefano Stabellini
Browse files

xen/mapcache: store dma information in revmapcache entries for debugging 



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.

Signed-off-by: default avatarStefano Stabellini <sstabellini@kernel.org>
Acked-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Acked-by: default avatarAnthony PERARD <anthony.perard@citrix.com>
parent cdece046

exec.c

+4 −4
Original line number Diff line number Diff line
@@ -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);

hw/i386/xen/xen-mapcache.c

+10 −5
Original line number Diff line number Diff line
@@ -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 +428,11 @@ 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);

    }

include/sysemu/xen-mapcache.h

+3 −2
Original line number Diff line number Diff line
@@ -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();

}