Re: [Xen-devel] [PATCH v3 1/3] x86/mm: Introduce altp2m_get_gfn_type_access

[Alexandru Stefan ISAILA <aisaila@xxxxxxxxxxxxxxx>]

On 09.04.2019 16:48, Tamas K Lengyel wrote:
> On Tue, Apr 9, 2019 at 6:04 AM Alexandru Stefan ISAILA
> <aisaila@xxxxxxxxxxxxxxx> wrote:
>>
>> This patch moves common code from p2m_set_altp2m_mem_access() and
>> p2m_change_altp2m_gfn() into one function
>>
>> Signed-off-by: Alexandru Isaila <aisaila@xxxxxxxxxxxxxxx>
>>
>> ---
>> Changes since V2:
>>          - Change var name from found_in_hostp2m to copied_from_hostp2m
>>          - Move the type check from altp2m_get_gfn_type_access() to the
>>          callers.
>> ---
>>   xen/arch/x86/mm/mem_access.c | 32 ++++++++++++----------------
>>   xen/arch/x86/mm/p2m.c        | 41 ++++++++++++++----------------------
>>   xen/include/asm-x86/p2m.h    | 19 +++++++++++++++++
>>   3 files changed, 49 insertions(+), 43 deletions(-)
>>
>> diff --git a/xen/arch/x86/mm/mem_access.c b/xen/arch/x86/mm/mem_access.c
>> index 56c06a4fc6..bf67ddb15a 100644
>> --- a/xen/arch/x86/mm/mem_access.c
>> +++ b/xen/arch/x86/mm/mem_access.c
>> @@ -265,31 +265,27 @@ int p2m_set_altp2m_mem_access(struct domain *d, struct 
>> p2m_domain *hp2m,
>>       unsigned int page_order;
>>       unsigned long gfn_l = gfn_x(gfn);
>>       int rc;
>> +    bool copied_from_hostp2m;
>>
>> -    mfn = ap2m->get_entry(ap2m, gfn, &t, &old_a, 0, NULL, NULL);
>> +    mfn = altp2m_get_gfn_type_access(ap2m, gfn, &t, &old_a, &page_order, 
>> &copied_from_hostp2m);
>>
>> -    /* Check host p2m if no valid entry in alternate */
>>       if ( !mfn_valid(mfn) )
>> +        return -ESRCH;
>> +
>> +    /* If this is a superpage, copy that first */
>> +    if ( page_order != PAGE_ORDER_4K && copied_from_hostp2m )
>>       {
>> +        unsigned long mask = ~((1UL << page_order) - 1);
>> +        gfn_t gfn2 = _gfn(gfn_l & mask);
>> +        mfn_t mfn2 = _mfn(mfn_x(mfn) & mask);
>>
>> -        mfn = __get_gfn_type_access(hp2m, gfn_l, &t, &old_a,
>> -                                    P2M_ALLOC | P2M_UNSHARE, &page_order, 
>> 0);
>> +        /* Note: currently it is not safe to remap to a shared entry */
>> +        if ( t != p2m_ram_rw )
>> +            return -ESRCH;
>>
>> -        rc = -ESRCH;
>> -        if ( !mfn_valid(mfn) || t != p2m_ram_rw )
>> +        rc = ap2m->set_entry(ap2m, gfn2, mfn2, page_order, t, old_a, 1);
>> +        if ( rc )
>>               return rc;
>> -
>> -        /* If this is a superpage, copy that first */
>> -        if ( page_order != PAGE_ORDER_4K )
>> -        {
>> -            unsigned long mask = ~((1UL << page_order) - 1);
>> -            gfn_t gfn2 = _gfn(gfn_l & mask);
>> -            mfn_t mfn2 = _mfn(mfn_x(mfn) & mask);
>> -
>> -            rc = ap2m->set_entry(ap2m, gfn2, mfn2, page_order, t, old_a, 1);
>> -            if ( rc )
>> -                return rc;
>> -        }
>>       }
>>
>>       /*
>> diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
>> index b9bbb8f485..d38d7c29ca 100644
>> --- a/xen/arch/x86/mm/p2m.c
>> +++ b/xen/arch/x86/mm/p2m.c
>> @@ -2626,6 +2626,7 @@ int p2m_change_altp2m_gfn(struct domain *d, unsigned 
>> int idx,
>>       mfn_t mfn;
>>       unsigned int page_order;
>>       int rc = -EINVAL;
>> +    bool copied_from_hostp2m;
>>
>>       if ( idx >= MAX_ALTP2M || d->arch.altp2m_eptp[idx] == 
>> mfn_x(INVALID_MFN) )
>>           return rc;
>> @@ -2636,7 +2637,7 @@ int p2m_change_altp2m_gfn(struct domain *d, unsigned 
>> int idx,
>>       p2m_lock(hp2m);
>>       p2m_lock(ap2m);
>>
>> -    mfn = ap2m->get_entry(ap2m, old_gfn, &t, &a, 0, NULL, NULL);
>> +    mfn = altp2m_get_gfn_type_access(ap2m, old_gfn, &t, &a, &page_order, 
>> &copied_from_hostp2m);
>>
>>       if ( gfn_eq(new_gfn, INVALID_GFN) )
>>       {
>> @@ -2646,37 +2647,27 @@ int p2m_change_altp2m_gfn(struct domain *d, unsigned 
>> int idx,
>>           goto out;
>>       }
>>
>> -    /* Check host p2m if no valid entry in alternate */
>> -    if ( !mfn_valid(mfn) )
>> -    {
>> -        mfn = __get_gfn_type_access(hp2m, gfn_x(old_gfn), &t, &a,
>> -                                    P2M_ALLOC, &page_order, 0);
>> +    if ( !mfn_valid(mfn) || (t != p2m_ram_rw && copied_from_hostp2m) )
> 
> Is this check correct? Why do you want to get out only when type is
> non-rw *and* it's copied from the hostp2m? You could have non-rw
> entries like mmio in the altp2m that were lazily copied and I don't
> think we want to allow remapping to those either.

I just copied the functionality. If this is needed I will add a || t != 
p2m_mmio_dm and p2m_mmio_direct.

Alex

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