Re: [Xen-devel] [PATCH for-4.13] xen/arm: mm: Allow generic xen page-tables helpers to be called early

From: Julien Grall <julien.grall@arm.com>
To: Stefano Stabellini <sstabellini@kernel.org>
Cc: jgross@suse.com, Julien Grall <julien@xen.org>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Jan Beulich <JBeulich@suse.com>,
	xen-devel@lists.xenproject.org,
	Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
Subject: Re: [Xen-devel] [PATCH for-4.13] xen/arm: mm: Allow generic xen page-tables helpers to be called early
Date: Fri, 11 Oct 2019 14:33:56 +0100	[thread overview]
Message-ID: <6784a597-0865-5069-18be-4dc4197de7ff@arm.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1910101706350.9081@sstabellini-ThinkPad-T480s>

(+ Andrew and Jan)

Hi,

On 11/10/2019 01:27, Stefano Stabellini wrote:
> On Thu, 10 Oct 2019, Julien Grall wrote:
>> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
>> index be23acfe26..a6637ce347 100644
>> --- a/xen/arch/arm/mm.c
>> +++ b/xen/arch/arm/mm.c
>> @@ -964,11 +964,40 @@ static int create_xen_table(lpae_t *entry)
>>   
>>   static lpae_t *xen_map_table(mfn_t mfn)
>>   {
>> +    /*
>> +     * We may require to map the page table before map_domain_page() is
>> +     * useable. The requirements here is it must be useable as soon as
>> +     * page-tables are allocated dynamically via alloc_boot_pages().
>> +     *
>> +     * We need to do the check on physical address rather than virtual
>> +     * address to avoid truncation on Arm32. Therefore is_kernel() cannot
>> +     * be used.
>> +     */
>> +    if ( system_state == SYS_STATE_early_boot )
>> +    {
>> +        const mfn_t mstart = virt_to_mfn(_start);
>> +        const mfn_t mend = virt_to_mfn(_end);
>> +
>> +        if ( (mfn_x(mstart) <= mfn_x(mfn)) && (mfn_x(mfn) < mfn_x(mend)) )
>> +        {
> 
> The patch is good. Actually I noticed that we already have
> is_xen_fixed_mfn(), looks like it is made for this. I think we should
> use it here, except that is_xen_fixed_mfn has:

Thanks, I thought we had one but I couldn't remember the name :(.

> 
>       (mfn_to_maddr(mfn) <= virt_to_maddr(&_end)))
> 
> I think it should actually be:
> 
>       (mfn_to_maddr(mfn) < virt_to_maddr(&_end)))
> 
> Maybe we could fix that at the same time in one patch? However, it is
> the same definition as on x86, so I don't know what is going on there.

For Arm we should definitely use < and not <=.

I am assuming this is the same for x86. Andrew? Jan?

Cheers,

-- 
Julien Grall

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