Re: [PATCH 10/15] xen: Introduce the Xen mapcache

[Anthony Liguori <anthony@codemonkey.ws>]

On 08/12/2010 09:09 AM, stefano.stabellini@eu.citrix.com wrote:
> From: Anthony PERARD<anthony.perard@citrix.com>
>
> Introduce a mapcache to handle the 64bit address space of the guest
> from a 32bit userland process (Qemu).
> The mapcache maps chucks of guest memory on demand, unmaps them when
> they are not needed anymore.
>
> Signed-off-by: Anthony PERARD<anthony.perard@citrix.com>
> Signed-off-by: Stefano Stabellini<stefano.stabellini@eu.citrix.com>
> ---
>   hw/xen_machine_fv.c       |    7 ++
>   target-xen/qemu-xen.h     |   15 +++
>   target-xen/xen_mapcache.c |  233 +++++++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 255 insertions(+), 0 deletions(-)
>
> diff --git a/hw/xen_machine_fv.c b/hw/xen_machine_fv.c
> index b1bc88d..58237d6 100644
> --- a/hw/xen_machine_fv.c
> +++ b/hw/xen_machine_fv.c
> @@ -84,6 +84,13 @@ static void xen_init_fv(ram_addr_t ram_size,
>           exit(1);
>       }
>
> +#if defined(__i386__) || defined(__x86_64__)
> +    if (qemu_map_cache_init()) {
> +        fprintf(stderr, "qemu_map_cache_init returned: error %d\n", errno);
> +        exit(-1);
> +    }
> +#endif
> +
>       xc_get_hvm_param(xen_xc, xen_domid, HVM_PARAM_IOREQ_PFN,&ioreq_pfn);
>       fprintf(stderr, "shared page at pfn %lx\n", ioreq_pfn);
>       shared_page = xc_map_foreign_range(xen_xc, xen_domid, XC_PAGE_SIZE,
> diff --git a/target-xen/qemu-xen.h b/target-xen/qemu-xen.h
> index 79a4638..e4a7030 100644
> --- a/target-xen/qemu-xen.h
> +++ b/target-xen/qemu-xen.h
> @@ -13,6 +13,21 @@
>
>   /* xen_mapcache.c */
>
> +#if (defined(__i386__) || defined(__x86_64__))&&  !defined(QEMU_TOOL)
> +#define MAPCACHE
> +
> +#if defined(__i386__)
> +#define MAX_MCACHE_SIZE    0x40000000 /* 1GB max for x86 */
> +#define MCACHE_BUCKET_SHIFT 16
> +#elif defined(__x86_64__)
> +#define MAX_MCACHE_SIZE    0x1000000000 /* 64GB max for x86_64 */
> +#define MCACHE_BUCKET_SHIFT 20
> +#endif
> +
> +#define MCACHE_BUCKET_SIZE (1UL<<  MCACHE_BUCKET_SHIFT)
> +#endif
> +
> +int qemu_map_cache_init(void);
>   uint8_t *qemu_map_cache(target_phys_addr_t phys_addr, uint8_t lock);
>   void     qemu_invalidate_entry(uint8_t *buffer);
>   void     qemu_invalidate_map_cache(void);
> diff --git a/target-xen/xen_mapcache.c b/target-xen/xen_mapcache.c
> index 39daae2..efe036c 100644
> --- a/target-xen/xen_mapcache.c
> +++ b/target-xen/xen_mapcache.c
> @@ -1,5 +1,237 @@
> +#include "config.h"
> +
> +#include "hw/xen_backend.h"
>   #include "qemu-xen.h"
>
> +#include<xen/hvm/params.h>
> +#include<sys/mman.h>
> +
> +#if defined(MAPCACHE)
> +
> +#define BITS_PER_LONG (sizeof(long)*8)
> +#define BITS_TO_LONGS(bits) \
> +    (((bits)+BITS_PER_LONG-1)/BITS_PER_LONG)
> +#define DECLARE_BITMAP(name,bits) \
> +    unsigned long name[BITS_TO_LONGS(bits)]
> +#define test_bit(bit,map) \
> +    (!!((map)[(bit)/BITS_PER_LONG]&  (1UL<<  ((bit)%BITS_PER_LONG))))
> +
> +struct map_cache {
> +    unsigned long paddr_index;
> +    uint8_t      *vaddr_base;
> +    DECLARE_BITMAP(valid_mapping, MCACHE_BUCKET_SIZE>>XC_PAGE_SHIFT);
> +    uint8_t lock;
> +    struct map_cache *next;
> +};
> +
> +struct map_cache_rev {
> +    uint8_t      *vaddr_req;
> +    unsigned long paddr_index;
> +    QTAILQ_ENTRY(map_cache_rev) next;
> +};
>
>    

CODING_STYLE

> +static struct map_cache *mapcache_entry;
> +static unsigned long nr_buckets;
> +QTAILQ_HEAD(map_cache_head, map_cache_rev) locked_entries = QTAILQ_HEAD_INITIALIZER(locked_entries);
> +
> +/* For most cases (>99.9%), the page address is the same. */
> +static unsigned long last_address_index = ~0UL;
> +static uint8_t      *last_address_vaddr;
>    

Should refactor away global state.

> +int qemu_map_cache_init(void)
> +{
> +    unsigned long size;
> +
> +    nr_buckets = (((MAX_MCACHE_SIZE>>  XC_PAGE_SHIFT) +
> +                   (1UL<<  (MCACHE_BUCKET_SHIFT - XC_PAGE_SHIFT)) - 1)>>
> +                  (MCACHE_BUCKET_SHIFT - XC_PAGE_SHIFT));
> +
> +    /*
> +     * Use mmap() directly: lets us allocate a big hash table with no up-front
> +     * cost in storage space. The OS will allocate memory only for the buckets
> +     * that we actually use. All others will contain all zeroes.
> +     */
> +    size = nr_buckets * sizeof(struct map_cache);
> +    size = (size + XC_PAGE_SIZE - 1)&  ~(XC_PAGE_SIZE - 1);
> +    fprintf(stderr, "qemu_map_cache_init nr_buckets = %lx size %lu\n", nr_buckets, size);
> +    mapcache_entry = mmap(NULL, size, PROT_READ|PROT_WRITE,
> +                          MAP_SHARED|MAP_ANON, -1, 0);
> +    if (mapcache_entry == MAP_FAILED) {
> +        errno = ENOMEM;
> +        return -1;
> +    }
> +
> +    return 0;
> +}
> +
> +static void qemu_remap_bucket(struct map_cache *entry,
> +                              unsigned long address_index)
> +{
> +    uint8_t *vaddr_base;
> +    xen_pfn_t pfns[MCACHE_BUCKET_SIZE>>  XC_PAGE_SHIFT];
> +    int err[MCACHE_BUCKET_SIZE>>  XC_PAGE_SHIFT];
> +    unsigned int i, j;
> +
> +    if (entry->vaddr_base != NULL) {
> +        errno = munmap(entry->vaddr_base, MCACHE_BUCKET_SIZE);
> +        if (errno) {
> +            fprintf(stderr, "unmap fails %d\n", errno);
> +            exit(-1);
> +        }
> +    }
> +
> +    for (i = 0; i<  MCACHE_BUCKET_SIZE>>  XC_PAGE_SHIFT; i++) {
> +        pfns[i] = (address_index<<  (MCACHE_BUCKET_SHIFT-XC_PAGE_SHIFT)) + i;
> +    }
> +
> +    vaddr_base = xc_map_foreign_bulk(xen_xc, xen_domid, PROT_READ|PROT_WRITE,
> +                                     pfns, err,
> +                                     MCACHE_BUCKET_SIZE>>  XC_PAGE_SHIFT);
> +    if (vaddr_base == NULL) {
> +        fprintf(stderr, "xc_map_foreign_bulk error %d\n", errno);
> +        exit(-1);
> +    }
> +
> +    entry->vaddr_base  = vaddr_base;
> +    entry->paddr_index = address_index;
> +
> +    for (i = 0; i<  MCACHE_BUCKET_SIZE>>  XC_PAGE_SHIFT; i += BITS_PER_LONG) {
> +        unsigned long word = 0;
> +        j = ((i + BITS_PER_LONG)>  (MCACHE_BUCKET_SIZE>>  XC_PAGE_SHIFT)) ?
> +            (MCACHE_BUCKET_SIZE>>  XC_PAGE_SHIFT) % BITS_PER_LONG : BITS_PER_LONG;
> +        while (j>  0) {
> +            word = (word<<  1) | !err[i + --j];
> +        }
> +        entry->valid_mapping[i / BITS_PER_LONG] = word;
> +    }
> +}
> +
> +uint8_t *qemu_map_cache(target_phys_addr_t phys_addr, uint8_t lock)
> +{
> +    struct map_cache *entry, *pentry = NULL;
> +    unsigned long address_index  = phys_addr>>  MCACHE_BUCKET_SHIFT;
> +    unsigned long address_offset = phys_addr&  (MCACHE_BUCKET_SIZE-1);
> +
> +    if (address_index == last_address_index&&  !lock)
> +        return last_address_vaddr + address_offset;
> +
> +    entry =&mapcache_entry[address_index % nr_buckets];
> +
> +    while (entry&&  entry->lock&&  entry->paddr_index != address_index&&  entry->vaddr_base) {
> +        pentry = entry;
> +        entry = entry->next;
> +    }
> +    if (!entry) {
> +        entry = qemu_mallocz(sizeof(struct map_cache));
> +        pentry->next = entry;
> +        qemu_remap_bucket(entry, address_index);
> +    } else if (!entry->lock) {
> +        if (!entry->vaddr_base || entry->paddr_index != address_index || !test_bit(address_offset>>XC_PAGE_SHIFT, entry->valid_mapping))
> +            qemu_remap_bucket(entry, address_index);
> +    }
> +
> +    if (!test_bit(address_offset>>XC_PAGE_SHIFT, entry->valid_mapping)) {
> +        last_address_index = ~0UL;
> +        return NULL;
> +    }
> +
> +    last_address_index = address_index;
> +    last_address_vaddr = entry->vaddr_base;
> +    if (lock) {
> +        struct map_cache_rev *reventry = qemu_mallocz(sizeof(struct map_cache_rev));
> +        entry->lock++;
> +        reventry->vaddr_req = last_address_vaddr + address_offset;
> +        reventry->paddr_index = last_address_index;
> +        QTAILQ_INSERT_TAIL(&locked_entries, reventry, next);
> +    }
> +
> +    return last_address_vaddr + address_offset;
> +}
> +
> +void qemu_invalidate_entry(uint8_t *buffer)
> +{
> +    struct map_cache *entry = NULL, *pentry = NULL;
> +    struct map_cache_rev *reventry;
> +    unsigned long paddr_index;
> +    int found = 0;
> +
> +    if (last_address_vaddr == buffer)
> +        last_address_index =  ~0UL;
> +
> +    QTAILQ_FOREACH(reventry,&locked_entries, next) {
> +        if (reventry->vaddr_req == buffer) {
> +            paddr_index = reventry->paddr_index;
> +            found = 1;
> +            break;
> +        }
> +    }
> +    if (!found) {
> +        fprintf(stderr, "qemu_invalidate_entry: could not find %p\n", buffer);
> +        QTAILQ_FOREACH(reventry,&locked_entries, next) {
> +            fprintf(stderr, "   %lx ->  %p is present\n", reventry->paddr_index, reventry->vaddr_req);
> +        }
> +        return;
> +    }
> +    QTAILQ_REMOVE(&locked_entries, reventry, next);
> +    qemu_free(reventry);
> +
> +    entry =&mapcache_entry[paddr_index % nr_buckets];
> +    while (entry&&  entry->paddr_index != paddr_index) {
> +        pentry = entry;
> +        entry = entry->next;
> +    }
> +    if (!entry) {
> +        fprintf(stderr, "Trying to unmap address %p that is not in the mapcache!\n", buffer);
> +        return;
> +    }
> +    entry->lock--;
> +    if (entry->lock>  0 || pentry == NULL)
> +        return;
> +
> +    pentry->next = entry->next;
> +    errno = munmap(entry->vaddr_base, MCACHE_BUCKET_SIZE);
> +    if (errno) {
> +        fprintf(stderr, "unmap fails %d\n", errno);
> +        exit(-1);
> +    }
> +    qemu_free(entry);
> +}
> +
> +void qemu_invalidate_map_cache(void)
> +{
> +    unsigned long i;
> +    struct map_cache_rev *reventry;
> +
> +    qemu_aio_flush();
> +
> +    QTAILQ_FOREACH(reventry,&locked_entries, next) {
> +        fprintf(stderr, "There should be no locked mappings at this time, but %lx ->  %p is present\n", reventry->paddr_index, reventry->vaddr_req);
> +    }
> +
> +    mapcache_lock();
> +
> +    for (i = 0; i<  nr_buckets; i++) {
> +        struct map_cache *entry =&mapcache_entry[i];
> +
> +        if (entry->vaddr_base == NULL)
> +            continue;
> +
> +        errno = munmap(entry->vaddr_base, MCACHE_BUCKET_SIZE);
> +        if (errno) {
> +            fprintf(stderr, "unmap fails %d\n", errno);
> +            exit(-1);
> +        }
> +
> +        entry->paddr_index = 0;
> +        entry->vaddr_base  = NULL;
> +    }
> +
> +    last_address_index =  ~0UL;
> +    last_address_vaddr = NULL;
> +
> +    mapcache_unlock();
> +}
> +#else
>   uint8_t *qemu_map_cache(target_phys_addr_t phys_addr, uint8_t lock)
>   {
>       return phys_ram_addr(phys_addr);
> @@ -12,3 +244,4 @@ void qemu_invalidate_map_cache(void)
>   void qemu_invalidate_entry(uint8_t *buffer)
>   {
>   }
> +#endif /* !MAPCACHE */
>    

This should really tie into the RAMBlock infrastructure.

Regards,

Anthony Liguori