diff mbox series

[QEMU,PATCHv2,7/8] xen: add map and unmap callbacks for grant region

Message ID 20231025212422.30371-8-vikram.garhwal@amd.com (mailing list archive)
State New, archived
Headers show
Series [QEMU,PATCHv2,1/8] xen: when unplugging emulated devices skip virtio devices | expand

Commit Message

Vikram Garhwal Oct. 25, 2023, 9:24 p.m. UTC 
From: Juergen Gross <jgross@suse.com>

Add the callbacks for mapping/unmapping guest memory via grants to the
special grant memory region.

Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Vikram Garhwal <vikram.garhwal@amd.com>
---
 hw/xen/xen-mapcache.c | 175 +++++++++++++++++++++++++++++++++++++++++-
 system/physmem.c      |  11 ++-
 2 files changed, 181 insertions(+), 5 deletions(-)

Comments

Stefano Stabellini Oct. 26, 2023, 1:32 a.m. UTC | #1 
On Wed, 25 Oct 2023, Vikram Garhwal wrote:
> From: Juergen Gross <jgross@suse.com>
> 
> Add the callbacks for mapping/unmapping guest memory via grants to the
> special grant memory region.
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>
> Signed-off-by: Vikram Garhwal <vikram.garhwal@amd.com>
> ---
>  hw/xen/xen-mapcache.c | 175 +++++++++++++++++++++++++++++++++++++++++-
>  system/physmem.c      |  11 ++-
>  2 files changed, 181 insertions(+), 5 deletions(-)
> 
> diff --git a/hw/xen/xen-mapcache.c b/hw/xen/xen-mapcache.c
> index 8a61c7dde6..feb4a3b886 100644
> --- a/hw/xen/xen-mapcache.c
> +++ b/hw/xen/xen-mapcache.c
> @@ -9,6 +9,8 @@
>   */
>  
>  #include "qemu/osdep.h"
> +#include "qemu/queue.h"
> +#include "qemu/thread.h"
>  #include "qemu/units.h"
>  #include "qemu/error-report.h"
>  
> @@ -23,6 +25,8 @@
>  #include "sysemu/xen-mapcache.h"
>  #include "trace.h"
>  
> +#include <xenevtchn.h>
> +#include <xengnttab.h>
>  
>  //#define MAPCACHE_DEBUG
>  
> @@ -385,7 +389,7 @@ uint8_t *xen_map_cache(hwaddr phys_addr, hwaddr size,
>      return p;
>  }
>  
> -ram_addr_t xen_ram_addr_from_mapcache(void *ptr)
> +static ram_addr_t xen_ram_addr_from_mapcache_try(void *ptr)
>  {
>      MapCacheEntry *entry = NULL;
>      MapCacheRev *reventry;
> @@ -594,10 +598,178 @@ uint8_t *xen_replace_cache_entry(hwaddr old_phys_addr,
>      return p;
>  }
>  
> +struct XENMappedGrantRegion {
> +    void *addr;
> +    unsigned int pages;
> +    unsigned int refs;
> +    unsigned int prot;
> +    uint32_t idx;
> +    QLIST_ENTRY(XENMappedGrantRegion) list;
> +};
> +
> +static xengnttab_handle *xen_region_gnttabdev;
> +static QLIST_HEAD(GrantRegionList, XENMappedGrantRegion) xen_grant_mappings =
> +    QLIST_HEAD_INITIALIZER(xen_grant_mappings);
> +static QemuMutex xen_map_mutex;
> +
> +static void *xen_map_grant_dyn(MemoryRegion **mr, hwaddr addr, hwaddr *plen,
> +                               bool is_write, MemTxAttrs attrs)
> +{
> +    unsigned int page_off = addr & (XC_PAGE_SIZE - 1);
> +    unsigned int i;
> +    unsigned int total_grants = 0;
> +    unsigned int nrefs = (page_off + *plen + XC_PAGE_SIZE - 1) >> XC_PAGE_SHIFT;
> +    uint32_t ref = (addr - XEN_GRANT_ADDR_OFF) >> XC_PAGE_SHIFT;
> +    uint32_t *refs = NULL;
> +    unsigned int prot = PROT_READ;
> +    struct XENMappedGrantRegion *mgr = NULL;
> +
> +    if (is_write) {
> +        prot |= PROT_WRITE;
> +    }
> +
> +    qemu_mutex_lock(&xen_map_mutex);
> +
> +    QLIST_FOREACH(mgr, &xen_grant_mappings, list) {
> +        if (mgr->idx == ref &&
> +            mgr->pages == nrefs &&
> +            (mgr->prot & prot) == prot) {
> +            break;
> +        }
> +
> +        total_grants += mgr->pages;
> +    }
> +
> +    if (!mgr) {
> +        if (nrefs + total_grants >= XEN_MAX_VIRTIO_GRANTS) {
> +            return NULL;

missing qemu_mutex_unlock


> +        }
> +
> +        mgr = g_new(struct XENMappedGrantRegion, 1);
> +
> +        if (nrefs == 1) {
> +            refs = &ref;
> +        } else {
> +            refs = g_new(uint32_t, nrefs);
> +            for (i = 0; i < nrefs; i++) {
> +                refs[i] = ref + i;
> +            }
> +        }
> +        mgr->addr = xengnttab_map_domain_grant_refs(xen_region_gnttabdev, nrefs,
> +                                                    xen_domid, refs, prot);
> +        if (mgr->addr) {
> +            mgr->pages = nrefs;
> +            mgr->refs = 1;
> +            mgr->prot = prot;
> +            mgr->idx = ref;
> +
> +            QLIST_INSERT_HEAD(&xen_grant_mappings, mgr, list);
> +        } else {
> +            g_free(mgr);
> +            mgr = NULL;
> +        }
> +    } else {
> +        mgr->refs++;
> +    }
> +
> +    qemu_mutex_unlock(&xen_map_mutex);
> +
> +    if (nrefs > 1) {
> +        g_free(refs);
> +    }
> +
> +    return mgr ? mgr->addr + page_off : NULL;
> +}
> +
> +static void xen_unmap_grant_dyn(MemoryRegion *mr, void *buffer, ram_addr_t addr,
> +                                hwaddr len, bool is_write, hwaddr access_len)
> +{
> +    unsigned int page_off = (unsigned long)buffer & (XC_PAGE_SIZE - 1);
> +    unsigned int nrefs = (page_off + len + XC_PAGE_SIZE - 1) >> XC_PAGE_SHIFT;
> +    unsigned int prot = PROT_READ;
> +    struct XENMappedGrantRegion *mgr = NULL;
> +
> +    if (is_write) {
> +        prot |= PROT_WRITE;
> +    }
> +
> +    qemu_mutex_lock(&xen_map_mutex);
> +
> +    QLIST_FOREACH(mgr, &xen_grant_mappings, list) {
> +        if (mgr->addr == buffer - page_off &&
> +            mgr->pages == nrefs &&
> +            (mgr->prot & prot) == prot) {
> +            break;
> +        }
> +    }
> +    if (mgr) {
> +        mgr->refs--;
> +        if (!mgr->refs) {
> +            xengnttab_unmap(xen_region_gnttabdev, mgr->addr, nrefs);
> +
> +            QLIST_REMOVE(mgr, list);
> +            g_free(mgr);
> +        }
> +    } else {
> +        error_report("xen_unmap_grant_dyn() trying to unmap unknown buffer");
> +    }
> +
> +    qemu_mutex_unlock(&xen_map_mutex);
> +}
> +
> +static ram_addr_t xen_ram_addr_from_grant_cache(void *ptr)
> +{
> +    unsigned int page_off = (unsigned long)ptr & (XC_PAGE_SIZE - 1);
> +    struct XENMappedGrantRegion *mgr = NULL;
> +    ram_addr_t raddr = RAM_ADDR_INVALID;
> +
> +    qemu_mutex_lock(&xen_map_mutex);
> +
> +    QLIST_FOREACH(mgr, &xen_grant_mappings, list) {
> +        if (mgr->addr == ptr - page_off) {
> +            break;
> +        }
> +    }
> +
> +    if (mgr) {
> +        raddr = (mgr->idx << XC_PAGE_SHIFT) + page_off + XEN_GRANT_ADDR_OFF;
> +    }
> +
> +    qemu_mutex_unlock(&xen_map_mutex);
> +
> +    return raddr;
> +}
> +
> +ram_addr_t xen_ram_addr_from_mapcache(void *ptr)
> +{
> +    ram_addr_t raddr;
> +
> +    raddr = xen_ram_addr_from_mapcache_try(ptr);
> +    if (raddr == RAM_ADDR_INVALID) {
> +        raddr = xen_ram_addr_from_grant_cache(ptr);
> +    }
> +
> +    return raddr;
> +}
> +
> +static const struct MemoryRegionOps xen_grant_mr_ops = {
> +    .map = xen_map_grant_dyn,
> +    .unmap = xen_unmap_grant_dyn,
> +    .endianness = DEVICE_LITTLE_ENDIAN,
> +};
> +
>  MemoryRegion *xen_init_grant_ram(void)
>  {
>      RAMBlock *block;
>  
> +    qemu_mutex_init(&xen_map_mutex);
> +
> +    xen_region_gnttabdev = xengnttab_open(NULL, 0);
> +    if (xen_region_gnttabdev == NULL) {
> +        fprintf(stderr, "can't open gnttab device\n");
> +        return NULL;
> +    }
> +
>      memory_region_init(&ram_grants, NULL, "xen.grants",
>                         XEN_MAX_VIRTIO_GRANTS * XC_PAGE_SIZE);
>      block = g_malloc0(sizeof(*block));
> @@ -612,6 +784,7 @@ MemoryRegion *xen_init_grant_ram(void)
>      ram_grants.ram_block = block;
>      ram_grants.ram = true;
>      ram_grants.terminates = true;
> +    ram_grants.ops = &xen_grant_mr_ops;
>      ram_block_add_list(block);
>      memory_region_add_subregion(get_system_memory(), XEN_GRANT_ADDR_OFF,
>                                  &ram_grants);
> diff --git a/system/physmem.c b/system/physmem.c
> index 5db1b32823..155a8c05fb 100644
> --- a/system/physmem.c
> +++ b/system/physmem.c
> @@ -2233,13 +2233,16 @@ RAMBlock *qemu_ram_block_from_host(void *ptr, bool round_offset,
>  
>      if (xen_enabled()) {
>          ram_addr_t ram_addr;
> +
>          RCU_READ_LOCK_GUARD();
>          ram_addr = xen_ram_addr_from_mapcache(ptr);
> -        block = qemu_get_ram_block(ram_addr);
> -        if (block) {
> -            *offset = ram_addr - block->offset;
> +        if (ram_addr != RAM_ADDR_INVALID) {
> +            block = qemu_get_ram_block(ram_addr);
> +            if (block) {
> +                *offset = ram_addr - block->offset;
> +            }
> +            return block;
>          }
> -        return block;
>      }
>  
>      RCU_READ_LOCK_GUARD();
> -- 
> 2.17.1
>
Vikram Garhwal Oct. 26, 2023, 4:35 a.m. UTC | #2 
On Wed, Oct 25, 2023 at 06:32:26PM -0700, Stefano Stabellini wrote:
> On Wed, 25 Oct 2023, Vikram Garhwal wrote:
> > From: Juergen Gross <jgross@suse.com>
> > 
> > Add the callbacks for mapping/unmapping guest memory via grants to the
> > special grant memory region.
> > 
> > Signed-off-by: Juergen Gross <jgross@suse.com>
> > Signed-off-by: Vikram Garhwal <vikram.garhwal@amd.com>
> > ---
> >  hw/xen/xen-mapcache.c | 175 +++++++++++++++++++++++++++++++++++++++++-
> >  system/physmem.c      |  11 ++-
> >  2 files changed, 181 insertions(+), 5 deletions(-)
> > 
> > diff --git a/hw/xen/xen-mapcache.c b/hw/xen/xen-mapcache.c
> > index 8a61c7dde6..feb4a3b886 100644
> > --- a/hw/xen/xen-mapcache.c
> > +++ b/hw/xen/xen-mapcache.c
> > @@ -9,6 +9,8 @@
> >   */
> >  
> >  #include "qemu/osdep.h"
> > +#include "qemu/queue.h"
> > +#include "qemu/thread.h"
> >  #include "qemu/units.h"
> >  #include "qemu/error-report.h"
> >  
> > @@ -23,6 +25,8 @@
> >  #include "sysemu/xen-mapcache.h"
> >  #include "trace.h"
> >  
> > +#include <xenevtchn.h>
> > +#include <xengnttab.h>
> >  
> >  //#define MAPCACHE_DEBUG
> >  
> > @@ -385,7 +389,7 @@ uint8_t *xen_map_cache(hwaddr phys_addr, hwaddr size,
> >      return p;
> >  }
> >  
> > -ram_addr_t xen_ram_addr_from_mapcache(void *ptr)
> > +static ram_addr_t xen_ram_addr_from_mapcache_try(void *ptr)
> >  {
> >      MapCacheEntry *entry = NULL;
> >      MapCacheRev *reventry;
> > @@ -594,10 +598,178 @@ uint8_t *xen_replace_cache_entry(hwaddr old_phys_addr,
> >      return p;
> >  }
> >  
> > +struct XENMappedGrantRegion {
> > +    void *addr;
> > +    unsigned int pages;
> > +    unsigned int refs;
> > +    unsigned int prot;
> > +    uint32_t idx;
> > +    QLIST_ENTRY(XENMappedGrantRegion) list;
> > +};
> > +
> > +static xengnttab_handle *xen_region_gnttabdev;
> > +static QLIST_HEAD(GrantRegionList, XENMappedGrantRegion) xen_grant_mappings =
> > +    QLIST_HEAD_INITIALIZER(xen_grant_mappings);
> > +static QemuMutex xen_map_mutex;
> > +
> > +static void *xen_map_grant_dyn(MemoryRegion **mr, hwaddr addr, hwaddr *plen,
> > +                               bool is_write, MemTxAttrs attrs)
> > +{
> > +    unsigned int page_off = addr & (XC_PAGE_SIZE - 1);
> > +    unsigned int i;
> > +    unsigned int total_grants = 0;
> > +    unsigned int nrefs = (page_off + *plen + XC_PAGE_SIZE - 1) >> XC_PAGE_SHIFT;
> > +    uint32_t ref = (addr - XEN_GRANT_ADDR_OFF) >> XC_PAGE_SHIFT;
> > +    uint32_t *refs = NULL;
> > +    unsigned int prot = PROT_READ;
> > +    struct XENMappedGrantRegion *mgr = NULL;
> > +
> > +    if (is_write) {
> > +        prot |= PROT_WRITE;
> > +    }
> > +
> > +    qemu_mutex_lock(&xen_map_mutex);
> > +
> > +    QLIST_FOREACH(mgr, &xen_grant_mappings, list) {
> > +        if (mgr->idx == ref &&
> > +            mgr->pages == nrefs &&
> > +            (mgr->prot & prot) == prot) {
> > +            break;
> > +        }
> > +
> > +        total_grants += mgr->pages;
> > +    }
> > +
> > +    if (!mgr) {
> > +        if (nrefs + total_grants >= XEN_MAX_VIRTIO_GRANTS) {
> > +            return NULL;
> 
> missing qemu_mutex_unlock
Oops, thanks for catching this! Will fix it in v3.
> 
> 
> > +        }
> > +
> > +        mgr = g_new(struct XENMappedGrantRegion, 1);
> > +
> > +        if (nrefs == 1) {
> > +            refs = &ref;
> > +        } else {
> > +            refs = g_new(uint32_t, nrefs);
> > +            for (i = 0; i < nrefs; i++) {
> > +                refs[i] = ref + i;
> > +            }
> > +        }
> > +        mgr->addr = xengnttab_map_domain_grant_refs(xen_region_gnttabdev, nrefs,
> > +                                                    xen_domid, refs, prot);
> > +        if (mgr->addr) {
> > +            mgr->pages = nrefs;
> > +            mgr->refs = 1;
> > +            mgr->prot = prot;
> > +            mgr->idx = ref;
> > +
> > +            QLIST_INSERT_HEAD(&xen_grant_mappings, mgr, list);
> > +        } else {
> > +            g_free(mgr);
> > +            mgr = NULL;
> > +        }
> > +    } else {
> > +        mgr->refs++;
> > +    }
> > +
> > +    qemu_mutex_unlock(&xen_map_mutex);
> > +
> > +    if (nrefs > 1) {
> > +        g_free(refs);
> > +    }
> > +
> > +    return mgr ? mgr->addr + page_off : NULL;
> > +}
> > +
> > +static void xen_unmap_grant_dyn(MemoryRegion *mr, void *buffer, ram_addr_t addr,
> > +                                hwaddr len, bool is_write, hwaddr access_len)
> > +{
> > +    unsigned int page_off = (unsigned long)buffer & (XC_PAGE_SIZE - 1);
> > +    unsigned int nrefs = (page_off + len + XC_PAGE_SIZE - 1) >> XC_PAGE_SHIFT;
> > +    unsigned int prot = PROT_READ;
> > +    struct XENMappedGrantRegion *mgr = NULL;
> > +
> > +    if (is_write) {
> > +        prot |= PROT_WRITE;
> > +    }
> > +
> > +    qemu_mutex_lock(&xen_map_mutex);
> > +
> > +    QLIST_FOREACH(mgr, &xen_grant_mappings, list) {
> > +        if (mgr->addr == buffer - page_off &&
> > +            mgr->pages == nrefs &&
> > +            (mgr->prot & prot) == prot) {
> > +            break;
> > +        }
> > +    }
> > +    if (mgr) {
> > +        mgr->refs--;
> > +        if (!mgr->refs) {
> > +            xengnttab_unmap(xen_region_gnttabdev, mgr->addr, nrefs);
> > +
> > +            QLIST_REMOVE(mgr, list);
> > +            g_free(mgr);
> > +        }
> > +    } else {
> > +        error_report("xen_unmap_grant_dyn() trying to unmap unknown buffer");
> > +    }
> > +
> > +    qemu_mutex_unlock(&xen_map_mutex);
> > +}
> > +
> > +static ram_addr_t xen_ram_addr_from_grant_cache(void *ptr)
> > +{
> > +    unsigned int page_off = (unsigned long)ptr & (XC_PAGE_SIZE - 1);
> > +    struct XENMappedGrantRegion *mgr = NULL;
> > +    ram_addr_t raddr = RAM_ADDR_INVALID;
> > +
> > +    qemu_mutex_lock(&xen_map_mutex);
> > +
> > +    QLIST_FOREACH(mgr, &xen_grant_mappings, list) {
> > +        if (mgr->addr == ptr - page_off) {
> > +            break;
> > +        }
> > +    }
> > +
> > +    if (mgr) {
> > +        raddr = (mgr->idx << XC_PAGE_SHIFT) + page_off + XEN_GRANT_ADDR_OFF;
> > +    }
> > +
> > +    qemu_mutex_unlock(&xen_map_mutex);
> > +
> > +    return raddr;
> > +}
> > +
> > +ram_addr_t xen_ram_addr_from_mapcache(void *ptr)
> > +{
> > +    ram_addr_t raddr;
> > +
> > +    raddr = xen_ram_addr_from_mapcache_try(ptr);
> > +    if (raddr == RAM_ADDR_INVALID) {
> > +        raddr = xen_ram_addr_from_grant_cache(ptr);
> > +    }
> > +
> > +    return raddr;
> > +}
> > +
> > +static const struct MemoryRegionOps xen_grant_mr_ops = {
> > +    .map = xen_map_grant_dyn,
> > +    .unmap = xen_unmap_grant_dyn,
> > +    .endianness = DEVICE_LITTLE_ENDIAN,
> > +};
> > +
> >  MemoryRegion *xen_init_grant_ram(void)
> >  {
> >      RAMBlock *block;
> >  
> > +    qemu_mutex_init(&xen_map_mutex);
> > +
> > +    xen_region_gnttabdev = xengnttab_open(NULL, 0);
> > +    if (xen_region_gnttabdev == NULL) {
> > +        fprintf(stderr, "can't open gnttab device\n");
> > +        return NULL;
> > +    }
> > +
> >      memory_region_init(&ram_grants, NULL, "xen.grants",
> >                         XEN_MAX_VIRTIO_GRANTS * XC_PAGE_SIZE);
> >      block = g_malloc0(sizeof(*block));
> > @@ -612,6 +784,7 @@ MemoryRegion *xen_init_grant_ram(void)
> >      ram_grants.ram_block = block;
> >      ram_grants.ram = true;
> >      ram_grants.terminates = true;
> > +    ram_grants.ops = &xen_grant_mr_ops;
> >      ram_block_add_list(block);
> >      memory_region_add_subregion(get_system_memory(), XEN_GRANT_ADDR_OFF,
> >                                  &ram_grants);
> > diff --git a/system/physmem.c b/system/physmem.c
> > index 5db1b32823..155a8c05fb 100644
> > --- a/system/physmem.c
> > +++ b/system/physmem.c
> > @@ -2233,13 +2233,16 @@ RAMBlock *qemu_ram_block_from_host(void *ptr, bool round_offset,
> >  
> >      if (xen_enabled()) {
> >          ram_addr_t ram_addr;
> > +
> >          RCU_READ_LOCK_GUARD();
> >          ram_addr = xen_ram_addr_from_mapcache(ptr);
> > -        block = qemu_get_ram_block(ram_addr);
> > -        if (block) {
> > -            *offset = ram_addr - block->offset;
> > +        if (ram_addr != RAM_ADDR_INVALID) {
> > +            block = qemu_get_ram_block(ram_addr);
> > +            if (block) {
> > +                *offset = ram_addr - block->offset;
> > +            }
> > +            return block;
> >          }
> > -        return block;
> >      }
> >  
> >      RCU_READ_LOCK_GUARD();
> > -- 
> > 2.17.1
> >
diff mbox series

Patch

diff --git a/hw/xen/xen-mapcache.c b/hw/xen/xen-mapcache.c
index 8a61c7dde6..feb4a3b886 100644
--- a/hw/xen/xen-mapcache.c
+++ b/hw/xen/xen-mapcache.c
@@ -9,6 +9,8 @@ 
  */
 
 #include "qemu/osdep.h"
+#include "qemu/queue.h"
+#include "qemu/thread.h"
 #include "qemu/units.h"
 #include "qemu/error-report.h"
 
@@ -23,6 +25,8 @@ 
 #include "sysemu/xen-mapcache.h"
 #include "trace.h"
 
+#include <xenevtchn.h>
+#include <xengnttab.h>
 
 //#define MAPCACHE_DEBUG
 
@@ -385,7 +389,7 @@  uint8_t *xen_map_cache(hwaddr phys_addr, hwaddr size,
     return p;
 }
 
-ram_addr_t xen_ram_addr_from_mapcache(void *ptr)
+static ram_addr_t xen_ram_addr_from_mapcache_try(void *ptr)
 {
     MapCacheEntry *entry = NULL;
     MapCacheRev *reventry;
@@ -594,10 +598,178 @@  uint8_t *xen_replace_cache_entry(hwaddr old_phys_addr,
     return p;
 }
 
+struct XENMappedGrantRegion {
+    void *addr;
+    unsigned int pages;
+    unsigned int refs;
+    unsigned int prot;
+    uint32_t idx;
+    QLIST_ENTRY(XENMappedGrantRegion) list;
+};
+
+static xengnttab_handle *xen_region_gnttabdev;
+static QLIST_HEAD(GrantRegionList, XENMappedGrantRegion) xen_grant_mappings =
+    QLIST_HEAD_INITIALIZER(xen_grant_mappings);
+static QemuMutex xen_map_mutex;
+
+static void *xen_map_grant_dyn(MemoryRegion **mr, hwaddr addr, hwaddr *plen,
+                               bool is_write, MemTxAttrs attrs)
+{
+    unsigned int page_off = addr & (XC_PAGE_SIZE - 1);
+    unsigned int i;
+    unsigned int total_grants = 0;
+    unsigned int nrefs = (page_off + *plen + XC_PAGE_SIZE - 1) >> XC_PAGE_SHIFT;
+    uint32_t ref = (addr - XEN_GRANT_ADDR_OFF) >> XC_PAGE_SHIFT;
+    uint32_t *refs = NULL;
+    unsigned int prot = PROT_READ;
+    struct XENMappedGrantRegion *mgr = NULL;
+
+    if (is_write) {
+        prot |= PROT_WRITE;
+    }
+
+    qemu_mutex_lock(&xen_map_mutex);
+
+    QLIST_FOREACH(mgr, &xen_grant_mappings, list) {
+        if (mgr->idx == ref &&
+            mgr->pages == nrefs &&
+            (mgr->prot & prot) == prot) {
+            break;
+        }
+
+        total_grants += mgr->pages;
+    }
+
+    if (!mgr) {
+        if (nrefs + total_grants >= XEN_MAX_VIRTIO_GRANTS) {
+            return NULL;
+        }
+
+        mgr = g_new(struct XENMappedGrantRegion, 1);
+
+        if (nrefs == 1) {
+            refs = &ref;
+        } else {
+            refs = g_new(uint32_t, nrefs);
+            for (i = 0; i < nrefs; i++) {
+                refs[i] = ref + i;
+            }
+        }
+        mgr->addr = xengnttab_map_domain_grant_refs(xen_region_gnttabdev, nrefs,
+                                                    xen_domid, refs, prot);
+        if (mgr->addr) {
+            mgr->pages = nrefs;
+            mgr->refs = 1;
+            mgr->prot = prot;
+            mgr->idx = ref;
+
+            QLIST_INSERT_HEAD(&xen_grant_mappings, mgr, list);
+        } else {
+            g_free(mgr);
+            mgr = NULL;
+        }
+    } else {
+        mgr->refs++;
+    }
+
+    qemu_mutex_unlock(&xen_map_mutex);
+
+    if (nrefs > 1) {
+        g_free(refs);
+    }
+
+    return mgr ? mgr->addr + page_off : NULL;
+}
+
+static void xen_unmap_grant_dyn(MemoryRegion *mr, void *buffer, ram_addr_t addr,
+                                hwaddr len, bool is_write, hwaddr access_len)
+{
+    unsigned int page_off = (unsigned long)buffer & (XC_PAGE_SIZE - 1);
+    unsigned int nrefs = (page_off + len + XC_PAGE_SIZE - 1) >> XC_PAGE_SHIFT;
+    unsigned int prot = PROT_READ;
+    struct XENMappedGrantRegion *mgr = NULL;
+
+    if (is_write) {
+        prot |= PROT_WRITE;
+    }
+
+    qemu_mutex_lock(&xen_map_mutex);
+
+    QLIST_FOREACH(mgr, &xen_grant_mappings, list) {
+        if (mgr->addr == buffer - page_off &&
+            mgr->pages == nrefs &&
+            (mgr->prot & prot) == prot) {
+            break;
+        }
+    }
+    if (mgr) {
+        mgr->refs--;
+        if (!mgr->refs) {
+            xengnttab_unmap(xen_region_gnttabdev, mgr->addr, nrefs);
+
+            QLIST_REMOVE(mgr, list);
+            g_free(mgr);
+        }
+    } else {
+        error_report("xen_unmap_grant_dyn() trying to unmap unknown buffer");
+    }
+
+    qemu_mutex_unlock(&xen_map_mutex);
+}
+
+static ram_addr_t xen_ram_addr_from_grant_cache(void *ptr)
+{
+    unsigned int page_off = (unsigned long)ptr & (XC_PAGE_SIZE - 1);
+    struct XENMappedGrantRegion *mgr = NULL;
+    ram_addr_t raddr = RAM_ADDR_INVALID;
+
+    qemu_mutex_lock(&xen_map_mutex);
+
+    QLIST_FOREACH(mgr, &xen_grant_mappings, list) {
+        if (mgr->addr == ptr - page_off) {
+            break;
+        }
+    }
+
+    if (mgr) {
+        raddr = (mgr->idx << XC_PAGE_SHIFT) + page_off + XEN_GRANT_ADDR_OFF;
+    }
+
+    qemu_mutex_unlock(&xen_map_mutex);
+
+    return raddr;
+}
+
+ram_addr_t xen_ram_addr_from_mapcache(void *ptr)
+{
+    ram_addr_t raddr;
+
+    raddr = xen_ram_addr_from_mapcache_try(ptr);
+    if (raddr == RAM_ADDR_INVALID) {
+        raddr = xen_ram_addr_from_grant_cache(ptr);
+    }
+
+    return raddr;
+}
+
+static const struct MemoryRegionOps xen_grant_mr_ops = {
+    .map = xen_map_grant_dyn,
+    .unmap = xen_unmap_grant_dyn,
+    .endianness = DEVICE_LITTLE_ENDIAN,
+};
+
 MemoryRegion *xen_init_grant_ram(void)
 {
     RAMBlock *block;
 
+    qemu_mutex_init(&xen_map_mutex);
+
+    xen_region_gnttabdev = xengnttab_open(NULL, 0);
+    if (xen_region_gnttabdev == NULL) {
+        fprintf(stderr, "can't open gnttab device\n");
+        return NULL;
+    }
+
     memory_region_init(&ram_grants, NULL, "xen.grants",
                        XEN_MAX_VIRTIO_GRANTS * XC_PAGE_SIZE);
     block = g_malloc0(sizeof(*block));
@@ -612,6 +784,7 @@  MemoryRegion *xen_init_grant_ram(void)
     ram_grants.ram_block = block;
     ram_grants.ram = true;
     ram_grants.terminates = true;
+    ram_grants.ops = &xen_grant_mr_ops;
     ram_block_add_list(block);
     memory_region_add_subregion(get_system_memory(), XEN_GRANT_ADDR_OFF,
                                 &ram_grants);
diff --git a/system/physmem.c b/system/physmem.c
index 5db1b32823..155a8c05fb 100644
--- a/system/physmem.c
+++ b/system/physmem.c
@@ -2233,13 +2233,16 @@  RAMBlock *qemu_ram_block_from_host(void *ptr, bool round_offset,
 
     if (xen_enabled()) {
         ram_addr_t ram_addr;
+
         RCU_READ_LOCK_GUARD();
         ram_addr = xen_ram_addr_from_mapcache(ptr);
-        block = qemu_get_ram_block(ram_addr);
-        if (block) {
-            *offset = ram_addr - block->offset;
+        if (ram_addr != RAM_ADDR_INVALID) {
+            block = qemu_get_ram_block(ram_addr);
+            if (block) {
+                *offset = ram_addr - block->offset;
+            }
+            return block;
         }
-        return block;
     }
 
     RCU_READ_LOCK_GUARD();