Re: [Xen-devel] [PATCH] ioemu: directly project all memory on x86_64

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

I don't really want the memory-size parameter back. What if we support
memory hotplug in future (e.g., we could do now if the guest decides to
balloon in some memory higher up in its memory map)?

Also I strongly suspect this breaks memory ballooning when the guest reduces
its memory reservation, as qemu will crash as soon as it tries to access a
non-existent guest page. Not only might this occur if the guest goes mad, or
if it is doing some type of memory probing and hence touches completely
unused gfns, but I know that it also happens sometimes legitimately after
ballooning memory down. Unfortunately I can't now remember what the scenario
is, but I do remember that I implemented changeset 14773 for a good reason!
Without that changeset, qemu would always crash soon after a large
balloon-down operation, and at the time we tracked it down and 14773 was
deemed the right approach to fix it. I'm now racking my brains to remember
what the cause was...

Anyway I don't see what getting rid of the mapcache fixes. If you want to
avoid capacity misses then turn it into a direct-map cache (1:1 hash
function) for x86_64.

 -- Keir

On 23/1/08 15:51, "Samuel Thibault" <samuel.thibault@xxxxxxxxxxxxx> wrote:

> ioemu: directly project all memory on x86_64
> On x86_64, we have enough virtual addressing space to just directly
> project all guest's physical memory. We still need to keep the map
> cache, however, for some random addressing uses like acpi.
> For this, we need to know the amount of memory, so let's have the domain
> builder always pass it, not only for ia64 (it's harmless anyway).
> 
> Signed-off-by: Samuel Thibault <samuel.thibault@xxxxxxxxxxxxx>
> 
> diff -r c364f80eb4b5 tools/ioemu/hw/xen_machine_fv.c
> --- a/tools/ioemu/hw/xen_machine_fv.c Wed Jan 23 13:27:21 2008 +0000
> +++ b/tools/ioemu/hw/xen_machine_fv.c Wed Jan 23 15:37:19 2008 +0000
> @@ -26,6 +26,52 @@
>  #include "vl.h"
>  #include <xen/hvm/params.h>
>  #include <sys/mman.h>
> +
> +#if defined(__x86_64__) || defined(__ia64__)
> +static void phys_ram_base_reinit(void)
> +{
> +    unsigned long nr_pages;
> +    xen_pfn_t *page_array;
> +    int i;
> +
> +    if (phys_ram_base)
> +        munmap(phys_ram_base, ram_size);
> +
> +    nr_pages = ram_size / XC_PAGE_SIZE;
> +
> +    page_array = (xen_pfn_t *)malloc(nr_pages * sizeof(xen_pfn_t));
> +    if (page_array == NULL) {
> +        fprintf(logfile, "malloc returned error %d\n", errno);
> +        exit(-1);
> +    }
> +
> +    for (i = 0; i < nr_pages; i++)
> +        page_array[i] = i;
> + 
> +#if defined(__ia64__)
> +    /* VTI will not use memory between 3G~4G, so we just pass a legal pfn
> +       to make QEMU map continuous virtual memory space */
> +    if (ram_size > MMIO_START) { 
> +        for (i = 0 ; i < (MEM_G >> XC_PAGE_SHIFT); i++)
> +            page_array[(MMIO_START >> XC_PAGE_SHIFT) + i] =
> +                (STORE_PAGE_START >> XC_PAGE_SHIFT);
> +    }
> +#endif
> +
> +    phys_ram_base = xc_map_foreign_batch(xc_handle, domid,
> +                                         PROT_READ|PROT_WRITE,
> +                                         page_array, nr_pages);
> +    if (phys_ram_base == 0) {
> +        fprintf(logfile, "xc_map_foreign_batch returned error %d\n", errno);
> +        exit(-1);
> +    }
> +    free(page_array);
> +
> +    fprintf(logfile, "%ldMB direct physical ram projection\n", ram_size >>
> 20);
> +}
> +#else
> +#define phys_ram_base_reinit() ((void)0)
> +#endif
>  
>  #if defined(MAPCACHE)
>  
> @@ -174,6 +220,8 @@ void qemu_invalidate_map_cache(void)
>      last_address_vaddr = NULL;
>  
>      mapcache_unlock();
> +
> +    phys_ram_base_reinit();
>  }
>  
>  #endif /* defined(MAPCACHE) */
> @@ -191,14 +239,10 @@ static void xen_init_fv(uint64_t ram_siz
>      extern void *shared_page;
>      extern void *buffered_io_page;
>  #ifdef __ia64__
> -    unsigned long nr_pages;
> -    xen_pfn_t *page_array;
>      extern void *buffered_pio_page;
> -    int i;
>  #endif
>  
>  #if defined(__i386__) || defined(__x86_64__)
> -
>      if (qemu_map_cache_init()) {
>          fprintf(logfile, "qemu_map_cache_init returned: error %d\n", errno);
>          exit(-1);
> @@ -232,35 +276,9 @@ static void xen_init_fv(uint64_t ram_siz
>          fprintf(logfile, "map buffered PIO page returned error %d\n", errno);
>          exit(-1);
>      }
> +#endif
>  
> -    nr_pages = ram_size / XC_PAGE_SIZE;
> -
> -    page_array = (xen_pfn_t *)malloc(nr_pages * sizeof(xen_pfn_t));
> -    if (page_array == NULL) {
> -        fprintf(logfile, "malloc returned error %d\n", errno);
> -        exit(-1);
> -    }
> -
> -    for (i = 0; i < nr_pages; i++)
> -        page_array[i] = i;
> - 
> -    /* VTI will not use memory between 3G~4G, so we just pass a legal pfn
> -       to make QEMU map continuous virtual memory space */
> -    if (ram_size > MMIO_START) { 
> -        for (i = 0 ; i < (MEM_G >> XC_PAGE_SHIFT); i++)
> -            page_array[(MMIO_START >> XC_PAGE_SHIFT) + i] =
> -                (STORE_PAGE_START >> XC_PAGE_SHIFT);
> -    }
> -
> -    phys_ram_base = xc_map_foreign_batch(xc_handle, domid,
> -                                         PROT_READ|PROT_WRITE,
> -                                         page_array, nr_pages);
> -    if (phys_ram_base == 0) {
> -        fprintf(logfile, "xc_map_foreign_batch returned error %d\n", errno);
> -        exit(-1);
> -    }
> -    free(page_array);
> -#endif
> +    phys_ram_base_reinit();
>  
>      timeoffset_get();
>  
> diff -r c364f80eb4b5 tools/ioemu/target-i386-dm/exec-dm.c
> --- a/tools/ioemu/target-i386-dm/exec-dm.c Wed Jan 23 13:27:21 2008 +0000
> +++ b/tools/ioemu/target-i386-dm/exec-dm.c Wed Jan 23 15:37:19 2008 +0000
> @@ -411,10 +411,12 @@ int iomem_index(target_phys_addr_t addr)
>          return 0;
>  }
>  
> -#if defined(__i386__) || defined(__x86_64__)
> +#if defined(__i386__)
>  #define phys_ram_addr(x) (qemu_map_cache(x))
> +#elif defined(__x86_64__)
> +#define phys_ram_addr(x) (((x) < ram_size) ? (phys_ram_base + (x)) :
> qemu_map_cache(x))
>  #elif defined(__ia64__)
> -#define phys_ram_addr(x) ((addr < ram_size) ? (phys_ram_base + (x)) : NULL)
> +#define phys_ram_addr(x) (((x) < ram_size) ? (phys_ram_base + (x)) : NULL)
>  #endif
>  
>  extern unsigned long *logdirty_bitmap;
> diff -r c364f80eb4b5 tools/python/xen/xend/image.py
> --- a/tools/python/xen/xend/image.py Wed Jan 23 13:27:21 2008 +0000
> +++ b/tools/python/xen/xend/image.py Wed Jan 23 15:37:19 2008 +0000
> @@ -186,6 +186,9 @@ class ImageHandler:
>      # xm config file
>      def parseDeviceModelArgs(self, vmConfig):
>          ret = ["-domain-name", str(self.vm.info['name_label'])]
> +
> +        ret.append("-m")
> +        ret.append("%s" % (self.getRequiredInitialReservation() / 1024))
>  
>          # Find RFB console device, and if it exists, make QEMU enable
>          # the VNC console.
> @@ -565,12 +568,6 @@ class IA64_HVM_ImageHandler(HVMImageHand
>          # Explicit shadow memory is not a concept
>          return 0
>  
> -    def getDeviceModelArgs(self, restore = False):
> -        args = HVMImageHandler.getDeviceModelArgs(self, restore)
> -        args = args + ([ "-m", "%s" %
> -                         (self.getRequiredInitialReservation() / 1024) ])
> -        return args
> -
>  
>  class IA64_Linux_ImageHandler(LinuxImageHandler):
>  
> 
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> http://lists.xensource.com/xen-devel



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