Re: [PATCH v4 13/26] x86/boot: Split trampoline and pt init code

[Evgeniy Baskov <baskov@ispras.ru>]

On 2023-03-10 17:56, Ard Biesheuvel wrote:
> On Thu, 15 Dec 2022 at 13:40, Evgeniy Baskov <baskov@ispras.ru> wrote:
>> 
>> When allocating trampoline from libstub trampoline allocation is
>> performed separately, so it needs to be skipped.
>> 
>> Split trampoline initialization and allocation code into two
>> functions to make them invokable separately.
>> 
>> Tested-by: Mario Limonciello <mario.limonciello@amd.com>
>> Tested-by: Peter Jones <pjones@redhat.com>
>> Signed-off-by: Evgeniy Baskov <baskov@ispras.ru>
>> ---
>>  arch/x86/boot/compressed/pgtable_64.c | 73 
>> +++++++++++++++++----------
>>  1 file changed, 46 insertions(+), 27 deletions(-)
>> 
>> diff --git a/arch/x86/boot/compressed/pgtable_64.c 
>> b/arch/x86/boot/compressed/pgtable_64.c
>> index c7cf5a1059a8..1f7169248612 100644
>> --- a/arch/x86/boot/compressed/pgtable_64.c
>> +++ b/arch/x86/boot/compressed/pgtable_64.c
>> @@ -106,12 +106,8 @@ static unsigned long 
>> find_trampoline_placement(void)
>>         return bios_start - TRAMPOLINE_32BIT_SIZE;
>>  }
>> 
>> -struct paging_config paging_prepare(void *rmode)
>> +bool trampoline_pgtable_init(struct boot_params *boot_params)
>>  {
>> -       struct paging_config paging_config = {};
>> -
>> -       /* Initialize boot_params. Required for 
>> cmdline_find_option_bool(). */
>> -       boot_params = rmode;
>> 
>>         /*
>>          * Check if LA57 is desired and supported.
>> @@ -125,26 +121,10 @@ struct paging_config paging_prepare(void *rmode)
>>          *
>>          * That's substitute for boot_cpu_has() in early boot code.
>>          */
>> -       if (IS_ENABLED(CONFIG_X86_5LEVEL) &&
>> -                       !cmdline_find_option_bool("no5lvl") &&
>> -                       native_cpuid_eax(0) >= 7 &&
>> -                       (native_cpuid_ecx(7) & (1 << (X86_FEATURE_LA57 
>> & 31)))) {
>> -               paging_config.l5_required = 1;
>> -       }
>> -
>> -       paging_config.trampoline_start = find_trampoline_placement();
>> -
>> -       trampoline_32bit = (unsigned long 
>> *)paging_config.trampoline_start;
>> -
>> -       /* Preserve trampoline memory */
>> -       memcpy(trampoline_save, trampoline_32bit, 
>> TRAMPOLINE_32BIT_SIZE);
>> -
>> -       /* Clear trampoline memory first */
>> -       memset(trampoline_32bit, 0, TRAMPOLINE_32BIT_SIZE);
>> -
>> -       /* Copy trampoline code in place */
>> -       memcpy(trampoline_32bit + TRAMPOLINE_32BIT_CODE_OFFSET / 
>> sizeof(unsigned long),
>> -                       &trampoline_32bit_src, 
>> TRAMPOLINE_32BIT_CODE_SIZE);
>> +       bool l5_required = IS_ENABLED(CONFIG_X86_5LEVEL) &&
>> +                          !cmdline_find_option_bool("no5lvl") &&
>> +                          native_cpuid_eax(0) >= 7 &&
>> +                          (native_cpuid_ecx(7) & (1 << 
>> (X86_FEATURE_LA57 & 31)));
>> 
>>         /*
>>          * The code below prepares page table in trampoline memory.
>> @@ -160,10 +140,10 @@ struct paging_config paging_prepare(void *rmode)
>>          * We are not going to use the page table in trampoline memory 
>> if we
>>          * are already in the desired paging mode.
>>          */
>> -       if (paging_config.l5_required == !!(native_read_cr4() & 
>> X86_CR4_LA57))
>> +       if (l5_required == !!(native_read_cr4() & X86_CR4_LA57))
>>                 goto out;
>> 
>> -       if (paging_config.l5_required) {
>> +       if (l5_required) {
>>                 /*
>>                  * For 4- to 5-level paging transition, set up current 
>> CR3 as
>>                  * the first and the only entry in a new top-level 
>> page table.
>> @@ -185,6 +165,45 @@ struct paging_config paging_prepare(void *rmode)
>>                        (void *)src, PAGE_SIZE);
>>         }
>> 
>> +out:
>> +       return l5_required;
>> +}
>> +
>> +struct paging_config paging_prepare(void *rmode)
>> +{
>> +       struct paging_config paging_config = {};
>> +       bool early_trampoline_alloc = 0;
> 
> false
> 
>> +
>> +       /* Initialize boot_params. Required for 
>> cmdline_find_option_bool(). */
>> +       boot_params = rmode;
>> +
>> +       /*
>> +        * We only need to find trampoline placement, if we have
>> +        * not already done it from libstub.
>> +        */
>> +
>> +       paging_config.trampoline_start = find_trampoline_placement();
>> +       trampoline_32bit = (unsigned long 
>> *)paging_config.trampoline_start;
>> +       early_trampoline_alloc = 0;
>> +
> 
> false again
> 
> And it never becomes true, nor is it used anywhere else. Can we get rid 
> of it?

Yes, probably it is just a leftover of the approach I used
before. I'll remove that.
> 
>> +       /*
>> +        * Preserve trampoline memory.
>> +        * When trampoline is located in memory
>> +        * owned by us, i.e. allocated in EFISTUB,
>> +        * we don't care about previous contents
>> +        * of this memory so copying can also be skipped.
> 
> Can you please reflow comments so they takes up fewer lines?
> 

Will fix.

>> +        */
>> +       memcpy(trampoline_save, trampoline_32bit, 
>> TRAMPOLINE_32BIT_SIZE);
>> +
>> +       /* Clear trampoline memory first */
>> +       memset(trampoline_32bit, 0, TRAMPOLINE_32BIT_SIZE);
>> +
>> +       /* Copy trampoline code in place */
>> +       memcpy(trampoline_32bit + TRAMPOLINE_32BIT_CODE_OFFSET / 
>> sizeof(unsigned long),
>> +                       &trampoline_32bit_src, 
>> TRAMPOLINE_32BIT_CODE_SIZE);
>> +
>> +       paging_config.l5_required = 
>> trampoline_pgtable_init(boot_params);
>> +
>>  out:
>>         return paging_config;
>>  }
>> --
>> 2.37.4
>>