Re: [PATCH V7 1/2] xen/arm: Harden the P2M code in p2m_remove_mapping()

[Julien Grall <julien@xen.org>]

Hi Oleksandr,

On 16/07/2022 16:29, Oleksandr Tyshchenko wrote:
>> On 16/07/2022 15:56, Oleksandr Tyshchenko wrote:
>>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>>
>>> Borrow the x86's check from p2m_remove_page() which was added
>>> by the following commit: c65ea16dbcafbe4fe21693b18f8c2a3c5d14600e
>>> "x86/p2m: don't assert that the passed in MFN matches for a remove"
>>> and adjust it to the Arm code base.
>>>
>>> Basically, this check will be strictly needed for the xenheap pages
>>> after applying a subsequent commit which will introduce xenheap based
>>> M2P approach on Arm. But, it will be a good opportunity to harden
>>> the P2M code for *every* RAM pages since it is possible to remove
>>> any GFN - MFN mapping currently on Arm (even with the wrong helpers).
>>>
>>> Suggested-by: Julien Grall <jgrall@amazon.com>
>>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>> ---
>>> You can find the corresponding discussion at:
>>> https://urldefense.com/v3/__https://lore.kernel.org/xen-devel/82d8bfe0-cb46-d303-6a60-2324dd76a1f7@xen.org/__;!!GF_29dbcQIUBPA!3a2u-XL4NvAzSMfz72LARrdWVFvq2In5ZpUdxP2cSt7bM8PgV7P_ZclZG2R-rE9PcosUHyqsKRNfVG2TiM9Tlg$
>>> [lore[.]kernel[.]org]
>>> https://urldefense.com/v3/__https://lore.kernel.org/xen-devel/1652294845-13980-2-git-send-email-olekstysh@gmail.com/__;!!GF_29dbcQIUBPA!3a2u-XL4NvAzSMfz72LARrdWVFvq2In5ZpUdxP2cSt7bM8PgV7P_ZclZG2R-rE9PcosUHyqsKRNfVG0kg7IZSA$
>>> [lore[.]kernel[.]org]
>>>
>>> Changes V6 -> V7:
>>>      - make this commit to be the first
>>>      - update commit description and add a comment in code
>>> ---
>>>    xen/arch/arm/p2m.c | 28 ++++++++++++++++++++++++++++
>>>    1 file changed, 28 insertions(+)
>>>
>>> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
>>> index d00c2e462a..2a0d383df4 100644
>>> --- a/xen/arch/arm/p2m.c
>>> +++ b/xen/arch/arm/p2m.c
>>> @@ -1308,11 +1308,39 @@ static inline int p2m_remove_mapping(struct
>>> domain *d,
>>>                                         mfn_t mfn)
>>>    {
>>>        struct p2m_domain *p2m = p2m_get_hostp2m(d);
>>> +    unsigned long i;
>>>        int rc;
>>>          p2m_write_lock(p2m);
>>> +    /*
>>> +     * Before removing the GFN - MFN mapping for any RAM pages make
>>> sure
>>> +     * that there is no difference between what is already mapped
>>> and what
>>> +     * is requested to be unmapped.
>>> +     * If they don't match bail out early. For instance, this could
>>> happen
>>> +     * if two CPUs are requesting to unmap the same P2M concurrently.
>>
>> Missing word: P2M *entry*
> 
> Yes. May I please ask, could this be done on the commit if this appears
> to be the last version?

I have committed the series with the same typo.

Cheers,

-- 
Julien Grall