linux-kernel - Re: [PATCH] Documentation/x86/boot.rst: minor improvement

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Date:   Mon, 31 Aug 2020 22:35:40 -0700
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Cao jin <caoj.fnst@...fujitsu.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, x86@...nel.org
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, corbet@....net
Subject: Re: [PATCH] Documentation/x86/boot.rst: minor improvement

If you are going to fix the language...

On 2020-08-31 22:25, Cao jin wrote:
> Sorry, I mis-copied 2 addresses. make sure they are CCed.
> 
> On 9/1/20 11:41 AM, Cao jin wrote:
>> Typo fix & file name update
>>
>> Signed-off-by: Cao jin <caoj.fnst@...fujitsu.com>
>> ---
>>  Documentation/x86/boot.rst | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/x86/boot.rst b/Documentation/x86/boot.rst
>> index 7fafc7ac00d7..c04afec90486 100644
>> --- a/Documentation/x86/boot.rst
>> +++ b/Documentation/x86/boot.rst
>> @@ -1379,7 +1379,7 @@ can be calculated as follows::
>>  In addition to read/modify/write the setup header of the struct
>>  boot_params as that of 16-bit boot protocol, the boot loader should
>>  also fill the additional fields of the struct boot_params as described
>> -in zero-page.txt.
>> +in zero-page.rst.
>>  
>>  After setting up the struct boot_params, the boot loader can load
>>  64-bit kernel in the same way as that of 16-bit boot protocol, but
>> @@ -1391,7 +1391,7 @@ In 64-bit boot protocol, the kernel is started by jumping to the
>>  
>>  At entry, the CPU must be in 64-bit mode with paging enabled.

(Paging enabled is redundant here.)

>>  The range with setup_header.init_size from start address of loaded
>> -kernel and zero page and command line buffer get ident mapping;
>> +kernel and zero page and command line buffer get identity mapping;

The range with setup_header.init_size from start address of the loaded kernel,
the zero page, and the command line buffer get identity-mapped, anda GDT must
be loaded with the descriptors for selectors __BOOT_CS(0x10) and
__BOOT_DS(0x18): both descriptors must be 4G flat segment with __BOOT_CS
having execute/read
permission and __BOOT_DS...

Also, it might be useful to take a look to see if other data structures, like
setup_data and the initrd also need to be in the identity map.

	-hpa