Re: [PATCH v4 12/14] xen/arm64: mm: Introduce helpers to prepare/enable/disable the identity mapping

From: Julien Grall <julien@xen.org>
To: Michal Orzel <michal.orzel@amd.com>, xen-devel@lists.xenproject.org
Cc: Luca.Fancellu@arm.com, Julien Grall <jgrall@amazon.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Bertrand Marquis <bertrand.marquis@arm.com>,
	Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
Subject: Re: [PATCH v4 12/14] xen/arm64: mm: Introduce helpers to prepare/enable/disable the identity mapping
Date: Fri, 27 Jan 2023 19:30:55 +0000	[thread overview]
Message-ID: <5c1428a5-155f-b582-75b2-395f88086d15@xen.org> (raw)
In-Reply-To: <ddbcb326-b158-daa4-e9d2-42c420983497@amd.com>

Hi Michal,

On 16/01/2023 08:53, Michal Orzel wrote:
> On 13/01/2023 11:11, Julien Grall wrote:
>> +static void __init prepare_boot_identity_mapping(void)
>> +{
>> +    paddr_t id_addr = virt_to_maddr(_start);
>> +    lpae_t pte;
>> +    DECLARE_OFFSETS(id_offsets, id_addr);
>> +
>> +    /*
>> +     * We will be re-using the boot ID tables. They may not have been
>> +     * zeroed but they should be unlinked. So it is fine to use
>> +     * clear_page().
>> +     */
>> +    clear_page(boot_first_id);
>> +    clear_page(boot_second_id);
>> +    clear_page(boot_third_id);
>> +
>> +    if ( id_offsets[0] != 0 )
>> +        panic("Cannot handled ID mapping above 512GB\n");
> I might be lost but didn't we say before that we can load Xen in the first 2TB?
> Then, how does this check correspond to it?

I forgot to change the check after we decided to extend the reserved 
area from 512GB to 2TB. I will update it in the next version.

Cheers,

-- 
Julien Grall