Re: [Qemu-devel] [PATCH for 2.9?] hmp: gpa2hva and gpa2hpa hostaddr command

[Paolo Bonzini <pbonzini@redhat.com>]

On 14/03/2017 18:57, Dr. David Alan Gilbert wrote:
> * Paolo Bonzini (pbonzini@redhat.com) wrote:
>> These commands are useful when testing machine-check passthrough.
>> gpa2hva is useful to inject a MADV_HWPOISON madvise from gdb, while
>> gpa2hpa is useful to inject an error with the mce-inject kernel
>> module.
>>
>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>> ---
>> 	Technically a feature, but on the other hand it is pretty
>> 	much impossible to test without it, and the people testing
>> 	the feature are using it as an out-of-tree patch.  Opinions?
> 
> I've no real objection except for the freeze; they're reasonable
> debug commands.
> 
>>  hmp-commands.hx |  32 ++++++++++++++++++
>>  monitor.c       | 103 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 135 insertions(+)
>>
>> diff --git a/hmp-commands.hx b/hmp-commands.hx
>> index 8819281..0aca984 100644
>> --- a/hmp-commands.hx
>> +++ b/hmp-commands.hx
>> @@ -526,6 +526,38 @@ Dump 80 16 bit values at the start of the video memory.
>>  ETEXI
>>  
>>      {
>> +        .name       = "gpa2hva",
>> +        .args_type  = "addr:l",
>> +        .params     = "addr",
>> +        .help       = "print the host virtual address corresponding to a guest physical address",
>> +        .cmd        = hmp_gpa2hva,
>> +    },
>> +
>> +STEXI
>> +@item gpa2hva @var{addr}
>> +@findex gpa2hva
>> +Print the host virtual address at which the guest's physical address @var{addr}
>> +is mapped.
>> +ETEXI
>> +
>> +#ifdef CONFIG_LINUX
>> +    {
>> +        .name       = "gpa2hpa",
>> +        .args_type  = "addr:l",
>> +        .params     = "addr",
>> +        .help       = "print the host physical address corresponding to a guest physical address",
>> +        .cmd        = hmp_gpa2hpa,
>> +    },
>> +#endif
>> +
>> +STEXI
>> +@item gpa2hpa @var{addr}
>> +@findex gpa2hpa
>> +Print the host physical address at which the guest's physical address @var{addr}
>> +is mapped.
>> +ETEXI
>> +
>> +    {
>>          .name       = "p|print",
>>          .args_type  = "fmt:/,val:l",
>>          .params     = "/fmt expr",
>> diff --git a/monitor.c b/monitor.c
>> index be282ec..1ac8c5f 100644
>> --- a/monitor.c
>> +++ b/monitor.c
>> @@ -1421,6 +1421,109 @@ static void hmp_physical_memory_dump(Monitor *mon, const QDict *qdict)
>>      memory_dump(mon, count, format, size, addr, 1);
>>  }
>>  
>> +static void *gpa2hva(MemoryRegion **p_mr, hwaddr addr, Error **errp)
>> +{
>> +    MemoryRegionSection mrs = memory_region_find(get_system_memory(),
>> +                                                 addr, 1);
>> +
>> +    if (!mrs.mr) {
>> +        error_setg(errp, "No memory is mapped at address 0x%" HWADDR_PRIx, addr);
>> +        return NULL;
>> +    }
>> +
>> +    if (!memory_region_is_ram(mrs.mr) && !memory_region_is_romd(mrs.mr)) {
>> +        error_setg(errp, "Memory at address 0x%" HWADDR_PRIx "is not RAM", addr);
>> +        memory_region_unref(mrs.mr);
>> +        return NULL;
>> +    }
>> +
>> +    *p_mr = mrs.mr;
>> +    return qemu_map_ram_ptr(mrs.mr->ram_block, mrs.offset_within_region);
>> +}
>> +
>> +static void hmp_gpa2hva(Monitor *mon, const QDict *qdict)
>> +{
>> +    hwaddr addr = qdict_get_int(qdict, "addr");
>> +    Error *local_err = NULL;
>> +    MemoryRegion *mr;
>> +    void *ptr;
>> +
>> +    ptr = gpa2hva(&mr, addr, &local_err);
>> +    if (local_err) {
>> +        error_report_err(local_err);
>> +        return;
>> +    }
>> +
>> +    monitor_printf(mon, "Host virtual address for 0x%" HWADDR_PRIx
>> +                   " (%s) is %p\n",
>> +                   addr, mr->name, ptr);
>> +
>> +    memory_region_unref(mr);
>> +}
>> +
>> +#ifdef CONFIG_LINUX
>> +static uint64_t vtop(void *ptr, Error **errp)
>> +{
>> +    uint64_t pinfo;
>> +    uint64_t ret = -1;
> 
> An odd value for a uint.

Call it an invalid physical address. :)

>> +    uintptr_t addr = (uintptr_t) ptr;
>> +    uintptr_t pagesize = getpagesize();
>> +    off_t offset = addr / pagesize * sizeof (pinfo);
>> +    char pagemapname[64];
>> +    int fd;
>> +
>> +    sprintf(pagemapname, "/proc/%d/pagemap", getpid());
>> +    fd = open(pagemapname, O_RDONLY);
> 
> /proc/self/pagemap would seem easier.

Ok.

>> +    if (fd == -1) {
>> +        error_setg_errno(errp, errno, "Cannot open %s", pagemapname);
>> +        return -1;
>> +    }
>> +
>> +    /* Force copy-on-write if necessary.  */
>> +    atomic_add((uint8_t *)ptr, 0);
>> +
>> +    if (pread(fd, &pinfo, sizeof(pinfo), offset) != sizeof(pinfo)) {
>> +        error_setg_errno(errp, errno, "Cannot read from %s", pagemapname);
>> +        goto out;
>> +    }
>> +    if ((pinfo & (1ull << 63)) == 0) {
>> +        error_setg(errp, "Page not present");
>> +        goto out;
>> +    }
>> +    ret = ((pinfo & 0x007fffffffffffffull) << 12) | (addr & (pagesize - 1));
> 
> Is that an x86 magic 12 ?
> (life would seem to get messy if pagesize != 1<<12 for that line)

Yes, it is.

Paolo