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

[Alexandru Stefan ISAILA <aisaila@xxxxxxxxxxxxxxx>]

On 09.04.2019 17:37, Tamas K Lengyel wrote:
> On Tue, Apr 9, 2019 at 8:03 AM Alexandru Stefan ISAILA
> <aisaila@xxxxxxxxxxxxxxx> wrote:
>>
>>
>>
>> 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.
> 
> My problem is with the && copied_form_hostp2m part. Why is that a criteria?

The (t != p2m_ram_rw) check was done only for the get from hostp2m.

If you think that I should do the check for all mfns (hostp2 and altp2m) 
then I can drop the copied_from_hostp2m bool and add mmio check.

I hope I understand the problem correctly.

Alex
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