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

[Evgeniy Baskov]

On 2023-03-10 17:56, Ard Biesheuvel wrote:
> On Thu, 15 Dec 2022 at 13:40, Evgeniy Baskov <baskov@xxxxxxxxx> 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@xxxxxxx>
> > Tested-by: Peter Jones <pjones@xxxxxxxxxx>
> > Signed-off-by: Evgeniy Baskov <baskov@xxxxxxxxx>
> > ---
> >  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