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Subject: Re: [PATCH v15 5/6] x86/boot: Parse SRAT address from RSDP and store
 immovable memory
To:     Kairui Song <kasong@redhat.com>,
        Chao Fan <fanc.fnst@cn.fujitsu.com>
Cc:     linux-kernel@vger.kernel.org, x86@kernel.org,
        Borislav Petkov <bp@alien8.de>, tglx@linutronix.de,
        mingo@redhat.com, hpa@zytor.com, Kees Cook <keescook@chromium.org>,
        Baoquan He <bhe@redhat.com>, msys.mizuma@gmail.com,
        indou.takao@jp.fujitsu.com, caoj.fnst@cn.fujitsu.com
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From:   Juergen Gross <jgross@suse.com>
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Date:   Thu, 17 Jan 2019 10:06:48 +0100
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On 17/01/2019 09:22, Kairui Song wrote:
> On Thu, Jan 17, 2019 at 3:58 PM Chao Fan <fanc.fnst@cn.fujitsu.com> wrote:
>>
>> On Wed, Jan 16, 2019 at 03:28:52PM +0800, Kairui Song wrote:
>>> On Mon, Jan 7, 2019 at 11:24 AM Chao Fan <fanc.fnst@cn.fujitsu.com> wrote:
>>>>
>>>> +
>>>> +/* Determine RSDP, based on acpi_os_get_root_pointer(). */
>>>> +static acpi_physical_address get_rsdp_addr(void)
>>>> +{
>>>> +       acpi_physical_address pa;
>>>> +
>>>> +       pa = get_acpi_rsdp();
>>>> +
>>>> +       if (!pa)
>>>> +               pa = efi_get_rsdp_addr();
>>>> +
>>>> +       if (!pa)
>>>> +               pa = bios_get_rsdp_addr();
>>>> +
>>>> +       return pa;
>>>> +}
>>>
>>> acpi_rsdp might be provided by boot_params.acpi_rsdp_addr too,
>>> it's introduced in ae7e1238e68f2a for Xen PVH guest and later move to
>>> boot_params in e6e094e053af,
>>> kexec could use it to pass RSDP to second kernel as well. Please check
>>> it as well make sure it always works.
>>>
>>
>> Hi Kairui,
>>
>> I saw the parsing code has been added to kernel, but I didn't see
>> where to fill in the 'acpi_rsdp_addr'. If only you(KEXEC) use it,
>> I can add "#ifdef CONFIG_KEXEC", but you said Xen will use it also,
>> so I didn't add ifdef to control it. I was trying to do as below:
>>
>> static inline acpi_physical_address get_boot_params_rsdp(void)
>> {
>>         return boot_params->acpi_rsdp_addr;
>> }
>>
>> static acpi_physical_address get_rsdp_addr(void)
>> {
>>         bool boot_params_rsdp_exist;
>>         acpi_physical_address pa;
>>
>>         pa = get_acpi_rsdp();
>>
>>         if (!pa)
>>                 pa = get_boot_params_rsdp();
>>
>>         if (!pa) {
>>                 pa = efi_get_rsdp_addr();
>>                 boot_params_rsdp_exist = false;
>>         }
>>         else
>>                 boot_params_rsdp_exist = true;
>>
>>         if (!pa)
>>                 pa = bios_get_rsdp_addr();
>>
>>         if (pa && !boot_params_rsdp_exist)
>>                 boot_params.acpi_rsdp_addr = pa;
>>
>>         return pa;
>> }
>>
>> At the same time, I notice kernel only parses it when
>> "#ifdef CONFIG_ACPI", we should keep sync with kernel, but I think
>> we are parsing SRAT, CONFIG_ACPI is needed sure, so I am going to
>> update the define of EARLY_SRAT_PARSE:
>>
>> config EARLY_SRAT_PARSE
>>         bool "EARLY SRAT parsing"
>>         def_bool y
>>         depends on RANDOMIZE_BASE && MEMORY_HOTREMOVE && ACPI
>>
>> Boris, how do you think the update for the new acpi_rsdp_addr?
>> If I misunderstand something, please let me know.
>>
>> Thanks,
>> Chao Fan
>>
> 
> Hi, thanks for considering kexec usage,
> 
> but I think "boot_params_rsdp_exist" is not necessary,
> boot_params->acpi_rsdp_addr should be either NULL or a valid value if
> I, later initialization code considers it a valid value if it's not
> NULL.
> 
> For the usage for Xen I'm not sure either, the info comes from commit
> message of ae7e1238e68f2a that's also where boot_params.acpi_rsdp_addr
> is first introduced, lets cc Juergen as well.

Thanks for adding me.

The Xen case is thought to prefer boot_params->acpi_rsdp_addr over all
other possibilities if set. This logic should be kept. It is used for
Xen PVH guests booted via grub2. Xen PVH guests don't have RSDP in low
memory, so this interface is needed.

In any case you should first try acpi_arch_get_root_pointer() as this
is the preferred way to override RSDP address.


Juergen