Re: [Qemu-devel] [PATCH 05/11 v10] Add API to get memory mapping

[HATAYAMA Daisuke]

From: Wen Congyang <address@hidden>
Subject: [PATCH 05/11 v10] Add API to get memory mapping
Date: Tue, 20 Mar 2012 11:51:18 +0800

> Add API to get all virtual address and physical address mapping.
> If the guest doesn't use paging, the virtual address is equal to the phyical
> address. The virtual address and physical address mapping is for gdb's user, 
> and
> it does not include the memory that is not referenced by the page table. So if
> you want to use crash to anaylze the vmcore, please do not specify -p option.
> the reason why the -p option is not default explicitly: guest machine in a
> catastrophic state can have corrupted memory, which we cannot trust.
> 
> Signed-off-by: Wen Congyang <address@hidden>
> ---
>  memory_mapping.c |   34 ++++++++++++++++++++++++++++++++++
>  memory_mapping.h |   15 +++++++++++++++
>  2 files changed, 49 insertions(+), 0 deletions(-)
> 
> diff --git a/memory_mapping.c b/memory_mapping.c
> index 718f271..b92e2f6 100644
> --- a/memory_mapping.c
> +++ b/memory_mapping.c
> @@ -164,3 +164,37 @@ void memory_mapping_list_init(MemoryMappingList *list)
>      list->last_mapping = NULL;
>      QTAILQ_INIT(&list->head);
>  }
> +
> +#if defined(CONFIG_HAVE_GET_MEMORY_MAPPING)
> +int qemu_get_guest_memory_mapping(MemoryMappingList *list)
> +{
> +    CPUArchState *env;
> +    RAMBlock *block;
> +    ram_addr_t offset, length;
> +    int ret;
> +    bool paging_mode;
> +
> +    paging_mode = cpu_paging_enabled(first_cpu);
> +    if (paging_mode) {

On SMP with (n)-CPUs, we can do this check at most (n)-times.

On Linux, user-mode tasks have differnet page tables. If refering to
one page table, we can get one user-mode task memory only. Considering
as much memory as possible, it's best to reference all CPUs with
paging enabled and walk all the page tables.

A problem is that linear addresses for user-mode tasks can inherently
conflicts. Different user-mode tasks can have the same linear
address. So, tools need to distinguish each PT_LOAD entry based on a
pair of linear address and physical address, not linear address
only. I don't know whether gdb does this.

> +        for (env = first_cpu; env != NULL; env = env->next_cpu) {
> +            ret = cpu_get_memory_mapping(list, env);
> +            if (ret < 0) {
> +                return -1;
> +            }
> +        }
> +        return 0;
> +    }
> +
> +    /*
> +     * If the guest doesn't use paging, the virtual address is equal to 
> physical
> +     * address.
> +     */

IIRC, ACPI sleep state goes in real-mode. There might be another that
can go in real-mode. If execution enters this path in such situation,
linear addresses are meaningless. But this is really rare case.

> +    QLIST_FOREACH(block, &ram_list.blocks, next) {
> +        offset = block->offset;
> +        length = block->length;
> +        create_new_memory_mapping(list, offset, offset, length);
> +    }
> +
> +    return 0;
> +}

Thanks.
HATAYAMA, Daisuke