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

[Wen Congyang <wency@cn.fujitsu.com>]

At 03/23/2012 08:02 PM, HATAYAMA Daisuke Wrote:
> From: Wen Congyang <wency@cn.fujitsu.com>
> 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 <wency@cn.fujitsu.com>
>> ---
>>  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.

gdb only can process kernel space. Jan's gdb-python script may can process
user-mode tasks, but we should get user-mode task's register from the kernel
or note, and convest virtual address/linear address to physicall address.

> 
>> +        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.

I donot meet such case, and I donot know what should I do in this patch now.
So I donot change it now.

Thanks
Wen Congyang

> 
>> +    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
> 
>