Re: [QEMU][PATCH v1 2/7] xen: add pseudo RAM region for grant mappings

[Stefano Stabellini]

On Mon, 9 Oct 2023, Stefano Stabellini wrote:
> On Thu, 5 Oct 2023, Vikram Garhwal wrote:
> > From: Juergen Gross <jgross@suse.com>
> > 
> > Add a memory region which can be used to automatically map granted
> > memory. It is starting at 0x8000000000000000ULL in order to be able to
> > distinguish it from normal RAM.
> > 
> > For this reason the xen.ram memory region is expanded, which has no
> > further impact as it is used just as a container of the real RAM
> > regions and now the grant region.
> > 
> > Signed-off-by: Juergen Gross <jgross@suse.com>
> > Signed-off-by: Vikram Garhwal <vikram.garhwal@amd.com>
> 
> This patch doesn't apply to staging anymore
> 
> 
> > ---
> >  hw/i386/xen/xen-hvm.c           |  3 ++
> >  hw/xen/xen-hvm-common.c         |  4 +--
> >  hw/xen/xen-mapcache.c           | 27 ++++++++++++++
> >  include/exec/ram_addr.h         |  1 +
> >  include/hw/xen/xen-hvm-common.h |  2 ++
> >  include/hw/xen/xen_pvdev.h      |  3 ++
> >  include/sysemu/xen-mapcache.h   |  3 ++
> >  softmmu/physmem.c               | 62 +++++++++++++++++++++------------
> >  8 files changed, 80 insertions(+), 25 deletions(-)
> > 
> > diff --git a/hw/i386/xen/xen-hvm.c b/hw/i386/xen/xen-hvm.c
> > index f42621e674..67a55558a6 100644
> > --- a/hw/i386/xen/xen-hvm.c
> > +++ b/hw/i386/xen/xen-hvm.c
> > @@ -172,6 +172,9 @@ static void xen_ram_init(PCMachineState *pcms,
> >                                   x86ms->above_4g_mem_size);
> >          memory_region_add_subregion(sysmem, 0x100000000ULL, &ram_hi);
> >      }
> > +
> > +    /* Add grant mappings as a pseudo RAM region. */
> > +    ram_grants = *xen_init_grant_ram();
> >  }
> >  
> >  static XenPhysmap *get_physmapping(hwaddr start_addr, ram_addr_t size)
> > diff --git a/hw/xen/xen-hvm-common.c b/hw/xen/xen-hvm-common.c
> > index 565dc39c8f..b7255977a5 100644
> > --- a/hw/xen/xen-hvm-common.c
> > +++ b/hw/xen/xen-hvm-common.c
> > @@ -9,7 +9,7 @@
> >  #include "hw/boards.h"
> >  #include "hw/xen/arch_hvm.h"
> >  
> > -MemoryRegion ram_memory;
> > +MemoryRegion ram_memory, ram_grants;
> >  
> >  void xen_ram_alloc(ram_addr_t ram_addr, ram_addr_t size, MemoryRegion *mr,
> >                     Error **errp)
> > @@ -26,7 +26,7 @@ void xen_ram_alloc(ram_addr_t ram_addr, ram_addr_t size, 
> > MemoryRegion *mr,
> >          return;
> >      }
> >  
> > -    if (mr == &ram_memory) {
> > +    if (mr == &ram_memory || mr == &ram_grants) {
> >          return;
> >      }
> >  
> > diff --git a/hw/xen/xen-mapcache.c b/hw/xen/xen-mapcache.c
> > index f7d974677d..8115c44c00 100644
> > --- a/hw/xen/xen-mapcache.c
> > +++ b/hw/xen/xen-mapcache.c
> > @@ -14,7 +14,9 @@
> >  
> >  #include <sys/resource.h>
> >  
> > +#include "hw/xen/xen-hvm-common.h"
> >  #include "hw/xen/xen_native.h"
> > +#include "hw/xen/xen_pvdev.h"
> >  #include "qemu/bitmap.h"
> >  
> >  #include "sysemu/runstate.h"
> > @@ -597,3 +599,28 @@ uint8_t *xen_replace_cache_entry(hwaddr old_phys_addr,
> >      mapcache_unlock();
> >      return p;
> >  }
> > +
> > +MemoryRegion *xen_init_grant_ram(void)
> > +{
> > +    RAMBlock *block;
> > +
> > +    memory_region_init(&ram_grants, NULL, "xen.grants",
> > +                       XEN_MAX_VIRTIO_GRANTS * XC_PAGE_SIZE);
> > +    block = g_malloc0(sizeof(*block));
> > +    block->mr = &ram_grants;
> > +    block->used_length = XEN_MAX_VIRTIO_GRANTS * XC_PAGE_SIZE;
> > +    block->max_length = XEN_MAX_VIRTIO_GRANTS * XC_PAGE_SIZE;
> > +    block->fd = -1;
> > +    block->page_size = XC_PAGE_SIZE;
> > +    block->host = (void *)XEN_GRANT_ADDR_OFF;
> > +    block->offset = XEN_GRANT_ADDR_OFF;
> > +    block->flags = RAM_PREALLOC;
> > +    ram_grants.ram_block = block;
> > +    ram_grants.ram = true;
> > +    ram_grants.terminates = true;
> > +    ram_block_add_list(block);
> > +    memory_region_add_subregion(get_system_memory(), XEN_GRANT_ADDR_OFF,
> > +                                &ram_grants);
> > +
> > +    return &ram_grants;
> 
> It doesn't look like xen_init_grant_ram has anything to do with the
> mapcache. It should be in another file. Maybe ./hw/xen/xen-hvm-common.c
> or ./hw/i386/xen/xen-hvm.c (but this is x86 specific and we need grants
> on ARM too)

Now having seen all the other patches, it might be OK to keep this here.
I am OK with this patch once it is rebased on the latest staging. I
would still advise to split the physdev.c changes to a separate patch.