Re: [Qemu-devel] [RFC PATCH 8/9] pc: adjust e820 map on hot-add and hot-remove

[Gleb Natapov]

On Thu, Apr 19, 2012 at 04:08:46PM +0200, Vasilis Liaskovitis wrote:
>  Hotplugged memory is not persistent in the e820 memory maps. After 
> hotplugging
>  a memslot and rebooting the VM, the hotplugged device is not present.
> 
>  A possible solution is to add an e820 for the new memslot in the acpi_piix4
>  hot-add handler. On a reset, Seabios (see next patch in series) will enable 
> all
>  memory devices for which it finds an e820 entry that covers the devices's 
> address
>  range.
> 
>  On hot-remove, the acpi_piix4 handler will try to remove the e820 entry
>  corresponding to the device. This will work when no VM reboots happen
>  between hot-add and hot-remove, but it is not a sufficient solution in
>  general: Seabios and GuestOS merge adjacent e820 entries on machine reboot,
>  so the sequence hot-add/ rebootVM / hot-remove will fail to remove a
>  corresponding e820 entry at the hot-remove phase.
> 
Why do you need this path and the next one? Bios can restore the state
of memslots and build e820 map by reading mems_sts.

>  Signed-off-by: Vasilis Liaskovitis <address@hidden>
> ---
>  hw/acpi_piix4.c |    6 ++++++
>  hw/pc.c         |   28 ++++++++++++++++++++++++++++
>  hw/pc.h         |    1 +
>  3 files changed, 35 insertions(+), 0 deletions(-)
> 
> diff --git a/hw/acpi_piix4.c b/hw/acpi_piix4.c
> index 2921d18..2b5fd04 100644
> --- a/hw/acpi_piix4.c
> +++ b/hw/acpi_piix4.c
> @@ -619,6 +619,9 @@ static void piix4_memslot_eject(uint32_t addr, uint32_t 
> val)
>              s = memslot_find_from_idx(start + idx);
>              assert(s != NULL);
>              memslot_depopulate(s);
> +            if (e820_del_entry(s->start, s->size, E820_RAM) == -EBUSY)
> +                PIIX4_DPRINTF("failed to remove e820 entry for memslot %u\n",
> +                       s->idx);
>          }
>          val = val >> 1;
>          idx++;
> @@ -634,6 +637,9 @@ static int piix4_memslot_hotplug(DeviceState *qdev, 
> SysBusDevice *dev, int
>  
>      if (add) {
>          enable_mem_device(s, slot->idx);
> +        if (e820_add_entry(slot->start, slot->size, E820_RAM) == -EBUSY)
> +            PIIX4_DPRINTF("failed to add e820 entry for memslot %u\n",
> +                    slot->idx);
>      }
>      else {
>          disable_mem_device(s, slot->idx);
> diff --git a/hw/pc.c b/hw/pc.c
> index f1f550a..04d243f 100644
> --- a/hw/pc.c
> +++ b/hw/pc.c
> @@ -593,6 +593,34 @@ int e820_add_entry(uint64_t address, uint64_t length, 
> uint32_t type)
>      return index;
>  }
>  
> +int e820_del_entry(uint64_t address, uint64_t length, uint32_t type)
> +{
> +    int index = le32_to_cpu(e820_table.count);
> +    int search;
> +    struct e820_entry *entry;
> +
> +    if (index == 0)
> +        return -EBUSY;
> +    search = index - 1;
> +    entry = &e820_table.entry[search];
> +    while (search >= 0) {
> +        if ((entry->address == cpu_to_le64(address)) &&
> +                (entry->length == cpu_to_le64(length)) &&
> +                (entry->type == cpu_to_le32(type))){
> +            if (search != index - 1) {
> +                memcpy(&e820_table.entry[search], &e820_table.entry[search + 
> 1],
> +                        sizeof(struct e820_entry) * (index - search));
> +            }
> +            index--;
> +            e820_table.count = cpu_to_le32(index);
> +            return 1;
> +        }
> +        search--;
> +        entry = &e820_table.entry[search];
> +    }
> +    return -EBUSY;
> +}
> +
>  static void bochs_bios_setup_hp_memslots(uint64_t *fw_cfg_slots);
>  
>  static void *bochs_bios_init(void)
> diff --git a/hw/pc.h b/hw/pc.h
> index 74d3369..4925e8c 100644
> --- a/hw/pc.h
> +++ b/hw/pc.h
> @@ -226,5 +226,6 @@ void pc_system_firmware_init(MemoryRegion *rom_memory);
>  #define E820_UNUSABLE   5
>  
>  int e820_add_entry(uint64_t, uint64_t, uint32_t);
> +int e820_del_entry(uint64_t, uint64_t, uint32_t);
>  
>  #endif
> -- 
> 1.7.9

--
                        Gleb.