Re: [Xen-devel] [PATCH v2 1/3] x86/mm: Introduce altp2m_get_gfn_type_access

[Alexandru Stefan ISAILA <aisaila@xxxxxxxxxxxxxxx>]

On 05.04.2019 18:04, Tamas K Lengyel wrote:
> On Fri, Apr 5, 2019 at 7:25 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>
>> ---
>>   xen/arch/x86/mm/mem_access.c | 30 +++++++++++------------------
>>   xen/arch/x86/mm/p2m.c        | 37 ++++++++++++++----------------------
>>   xen/include/asm-x86/p2m.h    | 23 ++++++++++++++++++++++
>>   3 files changed, 48 insertions(+), 42 deletions(-)
>>
>> diff --git a/xen/arch/x86/mm/mem_access.c b/xen/arch/x86/mm/mem_access.c
>> index 56c06a4fc6..608f748a57 100644
>> --- a/xen/arch/x86/mm/mem_access.c
>> +++ b/xen/arch/x86/mm/mem_access.c
>> @@ -265,31 +265,23 @@ 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 found_in_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, 
>> &found_in_hostp2m);
>>
>> -    /* Check host p2m if no valid entry in alternate */
>>       if ( !mfn_valid(mfn) )
>> -    {
>> +        return -ESRCH;
>>
>> -        mfn = __get_gfn_type_access(hp2m, gfn_l, &t, &old_a,
>> -                                    P2M_ALLOC | P2M_UNSHARE, &page_order, 
>> 0);
>> +    /* If this is a superpage, copy that first */
>> +    if ( page_order != PAGE_ORDER_4K && found_in_hostp2m )
>> +    {
>> +        unsigned long mask = ~((1UL << page_order) - 1);
>> +        gfn_t gfn2 = _gfn(gfn_l & mask);
>> +        mfn_t mfn2 = _mfn(mfn_x(mfn) & mask);
>>
>> -        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..b2a5c0c42e 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 found_in_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, 
>> &found_in_hostp2m);
>>
>>       if ( gfn_eq(new_gfn, INVALID_GFN) )
>>       {
>> @@ -2648,35 +2649,25 @@ int p2m_change_altp2m_gfn(struct domain *d, unsigned 
>> int idx,
>>
>>       /* 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 )
>> -            goto out;
>> +         goto out;
>>
>> -        /* If this is a superpage, copy that first */
>> -        if ( page_order != PAGE_ORDER_4K )
>> -        {
>> -            gfn_t gfn;
>> -            unsigned long mask;
>> +    /* If this is a superpage, copy that first */
>> +    if ( page_order != PAGE_ORDER_4K && found_in_hostp2m )
>> +    {
>> +        gfn_t gfn;
>> +        unsigned long mask;
>>
>> -            mask = ~((1UL << page_order) - 1);
>> -            gfn = _gfn(gfn_x(old_gfn) & mask);
>> -            mfn = _mfn(mfn_x(mfn) & mask);
>> +        mask = ~((1UL << page_order) - 1);
>> +        gfn = _gfn(gfn_x(old_gfn) & mask);
>> +        mfn = _mfn(mfn_x(mfn) & mask);
>>
>> -            if ( ap2m->set_entry(ap2m, gfn, mfn, page_order, t, a, 1) )
>> -                goto out;
>> -        }
>> +        if ( ap2m->set_entry(ap2m, gfn, mfn, page_order, t, a, 1) )
>> +            goto out;
>>       }
>>
>> -    mfn = ap2m->get_entry(ap2m, new_gfn, &t, &a, 0, NULL, NULL);
>> +    mfn = altp2m_get_gfn_type_access(ap2m, new_gfn, &t, &a, &page_order, 
>> &found_in_hostp2m);
>>
>>       if ( !mfn_valid(mfn) )
>> -        mfn = hp2m->get_entry(hp2m, new_gfn, &t, &a, 0, NULL, NULL);
>> -
>> -    /* Note: currently it is not safe to remap to a shared entry */
>> -    if ( !mfn_valid(mfn) || (t != p2m_ram_rw) )
>>           goto out;
>>
>>       if ( !ap2m->set_entry(ap2m, old_gfn, mfn, PAGE_ORDER_4K, t, a,
>> diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
>> index 2801a8ccca..42068b4aed 100644
>> --- a/xen/include/asm-x86/p2m.h
>> +++ b/xen/include/asm-x86/p2m.h
>> @@ -448,6 +448,29 @@ static inline mfn_t __nonnull(3) get_gfn_type(
>>       return get_gfn_type_access(p2m_get_hostp2m(d), gfn, t, &a, q, NULL);
>>   }
>>
>> +static inline mfn_t altp2m_get_gfn_type_access(
>> +    struct p2m_domain *ap2m, gfn_t gfn, p2m_type_t *t, p2m_access_t *a,
>> +    unsigned int *page_order, bool *found_in_hostp2m)
> 
> I don't like this. The way it's implemented is very convoluted and not
> consistent.
> 
>> +{
>> +    mfn_t mfn = ap2m->get_entry(ap2m, gfn, t, a, 0, NULL, NULL);
>> +
>> +    *found_in_hostp2m = false;
> 
> Just because an entry is in the altp2m now means it's not found in the
> hostp2m? Doesn't make sense.

The name of the var is not a good one I must agree. I tried to 
incorporate as much as the common code in one function.

The found_in_hostp2m var is used by the caller in the page_order != 
PAGE_ORDER_4K case.

> 
>> +
>> +    /* Check host p2m if no valid entry in alternate */
>> +    if ( !mfn_valid(mfn) )
>> +    {
>> +        mfn = __get_gfn_type_access(p2m_get_hostp2m(ap2m->domain), 
>> gfn_x(gfn), t, a,
>> +                                    P2M_ALLOC | P2M_UNSHARE, page_order, 
>> false);
>> +        *found_in_hostp2m = true;
> 
> Now it's found in the hostp2m, even if the mfn is invalid? Again,
> doesn't make sense.

I agree that the true comes here early and it can get true only if mfn 
is valid.

> 
>> +
>> +        /* Note: currently it is not safe to remap to a shared entry */
>> +        if ( !mfn_valid(mfn) || *t != p2m_ram_rw )
>> +            return INVALID_MFN;
> 
> This function is supposed to just get the type and access.. but
> instead it does sanity checks on the results that the caller is
> probably in a better position to judge. Again, inconsistent with the
> function's name and seemingly intended use.
> 

Ok I will get the check out of the function and let the caller.

About the found_in_hostp2m var, should it get a different name?

Regards,
Alex
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