Re: [Qemu-devel] [PATCH v2] hmp: gpa2hva and gpa2hpa hostaddr command

[Paolo Bonzini <pbonzini@redhat.com>]

On 20/03/2017 15:56, Peter Maydell wrote:
> On 20 March 2017 at 14:45, 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>
>> ---
>>  hmp-commands.hx |  32 ++++++++++++++++++
>>  monitor.c       | 101 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 133 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
> 
> I have some comments which feel kind of nit-picky, but since this
> is a public-facing HMP API I think they need attention since we only
> get one chance to get it right.
> 
>>      {
>> +        .name       = "gpa2hva",
>> +        .args_type  = "addr:l",
>> +        .params     = "addr",
>> +        .help       = "print the host virtual address corresponding to a guest physical address",
>> +        .cmd        = hmp_gpa2hva,
>> +    },
> 
> How does this work for guest CPUs which have more than one physical
> address space (eg ARM TrustZone)? There's no ability here to specify
> the secure/nonsecure transaction attribute that you need to distinguish
> which kind of guest physical address you're talking about.
> 
> The command also doesn't let you specify which CPU you care about,
> which is bad because they don't all have to have the same address map.

It just uses address_space_memory currently.  I can make it use the
current CPU address space too, similar to x and xp; it's the same for my
own use.

> The documentation should also say what happens if the guest physaddr
> doesn't correspond to RAM.

An error? :)

>> +#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.
> 
> ...what if you're on a system where host RAM exists at multiple host
> physical addresses?

It gives whatever the host OS thinks it's the corresponding host
physical address.  It's what happens to be in the page tables for the HVA.

> What if the RAM happens to be paged out?
> (Plus the remarks for gpa2hva apply.)

Another error? :)

Paolo