Re: [Qemu-devel] [PATCH v6 4/6] Add support for marking memory to not be migrated. On migration, memory is checked for the NO_MIGRATION_FLAG.

[Anthony Liguori]

On 06/04/2010 04:45 PM, Cam Macdonell wrote:
> This is useful for devices that do not want to take memory regions data with 
> them on migration.
> ---
>   arch_init.c  |   28 ++++++++++++++++------------
>   cpu-all.h    |    2 ++
>   cpu-common.h |    2 ++
>   exec.c       |   12 ++++++++++++
>   4 files changed, 32 insertions(+), 12 deletions(-)
>
> diff --git a/arch_init.c b/arch_init.c
> index cfc03ea..7a234fa 100644
> --- a/arch_init.c
> +++ b/arch_init.c
> @@ -118,18 +118,21 @@ static int ram_save_block(QEMUFile *f)
>                                               current_addr + TARGET_PAGE_SIZE,
>                                               MIGRATION_DIRTY_FLAG);
>
> -            p = qemu_get_ram_ptr(current_addr);
> -
> -            if (is_dup_page(p, *p)) {
> -                qemu_put_be64(f, current_addr | RAM_SAVE_FLAG_COMPRESS);
> -                qemu_put_byte(f, *p);
> -            } else {
> -                qemu_put_be64(f, current_addr | RAM_SAVE_FLAG_PAGE);
> -                qemu_put_buffer(f, p, TARGET_PAGE_SIZE);
> -            }
> +            if (!cpu_physical_memory_get_dirty(current_addr,
> +                                                    NO_MIGRATION_FLAG)) {
> +                p = qemu_get_ram_ptr(current_addr);
> +
> +                if (is_dup_page(p, *p)) {
> +                    qemu_put_be64(f, current_addr | RAM_SAVE_FLAG_COMPRESS);
> +                    qemu_put_byte(f, *p);
> +                } else {
> +                    qemu_put_be64(f, current_addr | RAM_SAVE_FLAG_PAGE);
> +                    qemu_put_buffer(f, p, TARGET_PAGE_SIZE);
> +                }
>
> -            found = 1;
> -            break;
> +                found = 1;
> +                break;
> +            }
>           }
>    

Shouldn't we just disable live migration out right?

I would rather that the device mark migration as impossible having the 
user hot remove the device before migration and then add it again after 
migration.  Device assignment could also use this functionality.

What this does is make migration possible but fundamentally broken which 
is not a good thing.

Regards,

Anthony Liguori

>           addr += TARGET_PAGE_SIZE;
>           current_addr = (saved_addr + addr) % last_ram_offset;
> @@ -146,7 +149,8 @@ static ram_addr_t ram_save_remaining(void)
>       ram_addr_t count = 0;
>
>       for (addr = 0; addr<  last_ram_offset; addr += TARGET_PAGE_SIZE) {
> -        if (cpu_physical_memory_get_dirty(addr, MIGRATION_DIRTY_FLAG)) {
> +        if (!cpu_physical_memory_get_dirty(addr, NO_MIGRATION_FLAG)&&
> +                cpu_physical_memory_get_dirty(addr, MIGRATION_DIRTY_FLAG)) {
>               count++;
>           }
>       }
> diff --git a/cpu-all.h b/cpu-all.h
> index 9080cc7..4df00ab 100644
> --- a/cpu-all.h
> +++ b/cpu-all.h
> @@ -887,6 +887,8 @@ extern int mem_prealloc;
>   #define CODE_DIRTY_FLAG      0x02
>   #define MIGRATION_DIRTY_FLAG 0x08
>
> +#define NO_MIGRATION_FLAG 0x10
> +
>   #define DIRTY_ALL_FLAG  (VGA_DIRTY_FLAG | CODE_DIRTY_FLAG | 
> MIGRATION_DIRTY_FLAG)
>
>   /* read dirty bit (return 0 or 1) */
> diff --git a/cpu-common.h b/cpu-common.h
> index 4b0ba60..a1ebbbe 100644
> --- a/cpu-common.h
> +++ b/cpu-common.h
> @@ -39,6 +39,8 @@ static inline void 
> cpu_register_physical_memory(target_phys_addr_t start_addr,
>       cpu_register_physical_memory_offset(start_addr, size, phys_offset, 0);
>   }
>
> +void cpu_mark_pages_no_migrate(ram_addr_t start, uint64_t size);
> +
>   ram_addr_t cpu_get_physical_page_desc(target_phys_addr_t addr);
>   ram_addr_t qemu_ram_map(ram_addr_t size, void *host);
>   ram_addr_t qemu_ram_alloc(ram_addr_t);
> diff --git a/exec.c b/exec.c
> index 39c18a7..c11d22f 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2786,6 +2786,18 @@ static void *file_ram_alloc(ram_addr_t memory, const 
> char *path)
>   }
>   #endif
>
> +void cpu_mark_pages_no_migrate(ram_addr_t start, uint64_t length)
> +{
> +    int i, len;
> +    uint8_t *p;
> +
> +    len = length>>  TARGET_PAGE_BITS;
> +    p = phys_ram_flags + (start>>  TARGET_PAGE_BITS);
> +    for (i = 0; i<  len; i++) {
> +        p[i] |= NO_MIGRATION_FLAG;
> +    }
> +}
> +
>   ram_addr_t qemu_ram_map(ram_addr_t size, void *host)
>   {
>       RAMBlock *new_block;
>