Re: [Xen-devel] [v6][PATCH 1/2] xen:x86:mm:p2m: introduce set_identity_p2m_entry

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 01.08.14 at 00:29, <kevin.tian@xxxxxxxxx> wrote:
>>  From: Chen, Tiejun
>> Sent: Tuesday, July 29, 2014 6:36 PM
>> 
>> Its used conveniently to create RMRR mapping in shared EPT case.
>> 
>> Signed-off-by: Tiejun Chen <tiejun.chen@xxxxxxxxx>
>> ---
>>  xen/arch/x86/mm/p2m.c     | 29 +++++++++++++++++++++++++++++
>>  xen/include/asm-x86/p2m.h |  3 +++
>>  2 files changed, 32 insertions(+)
>> 
>> v6:
>> 
>> * Refactor set_identity_p2m_entry to make sense
>> 
>> v5:
>> 
>> * Rename this function as set_identity_p2m_entry()
>> * Get mfn directly inside set_identity_p2m_entry()
>> 
>> v4:
>> 
>> * new patch to combine get and set together to create RMRR mapping.
>> 
>> diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
>> index 642ec28..06bed7a 100644
>> --- a/xen/arch/x86/mm/p2m.c
>> +++ b/xen/arch/x86/mm/p2m.c
>> @@ -858,6 +858,35 @@ int set_mmio_p2m_entry(struct domain *d, unsigned
>> long gfn, mfn_t mfn)
>>      return set_typed_p2m_entry(d, gfn, mfn, p2m_mmio_direct);
>>  }
>> 
>> +int set_identity_p2m_entry(struct domain *d, unsigned long gfn)
>> +{
>> +    p2m_type_t p2mt;
>> +    p2m_access_t a;
>> +    mfn_t mfn;
>> +    struct p2m_domain *p2m = p2m_get_hostp2m(d);
>> +    int ret = -EBUSY;
>> +
>> +    gfn_lock(p2m, gfn, 0);
>> +
>> +    mfn = p2m->get_entry(p2m, gfn, &p2mt, &a, 0, NULL);
>> +
>> +    if ( !mfn_valid(mfn) )
>> +        ret = p2m_set_entry(p2m, gfn, _mfn(gfn), PAGE_ORDER_4K,
>> p2m_mmio_direct,
>> +                            p2m_access_rw);
>> +    else if ( mfn_x(mfn) == gfn &&
>> +              p2mt == p2m_mmio_direct &&
>> +              a == p2m_access_rw )
>> +        ret = 0;
>> +    else
>> +        printk(XENLOG_G_WARNING
>> +               "Cannot identity map d%d:%lx, already mapped to %lx.\n",
>> +               d->domain_id, gfn, mfn_x(mfn));
> 
> what about !mfn_valid but the GFN has been used for emulated MMIOs? w/o
> a guest e820 view you can't avoid overlapping by just looking at mfn...

What good would looking at the guest's E820 table do here? Both
emulated MMIO ranges and the (supposed) exclusion ranges needed
for the RMRR would just be holes.

Jan


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