Re: [PATCH 4/6] x86/efi: Hoist page table switching code into efi_call_virt()

Matt Fleming
2015-11-12T20:15:48Z

On Thu, 12 Nov, at 07:47:14PM, Borislav Petkov wrote:
>
> checkpatch is bitching here - not that I agree with it:
>
> WARNING: please, no space before tabs
> #87: FILE: arch/x86/include/asm/efi.h:88:
> +^I^Iefi_scratch.prev_cr3 = read_cr3(); ^I^I^I\$
>
> WARNING: please, no space before tabs
> #89: FILE: arch/x86/include/asm/efi.h:90:
> +^I^I__flush_tlb_all(); ^I^I^I^I^I\$
>
> WARNING: please, no space before tabs
> #94: FILE: arch/x86/include/asm/efi.h:95:
> +^Iif (efi_scratch.use_pgd) { ^I^I^I^I^I\$
>
> WARNING: please, no space before tabs
> #96: FILE: arch/x86/include/asm/efi.h:97:
> +^I^I__flush_tlb_all(); ^I^I^I^I^I\$
>
> WARNING: please, no space before tabs
> #97: FILE: arch/x86/include/asm/efi.h:98:
> +^I} ^I^I^I^I^I^I^I^I\$

Crap. These look legit, I'll fix this up in v2.

> > diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
> > index 634536034e32..ab5f14a886cc 100644
> > --- a/arch/x86/platform/efi/efi_64.c
> > +++ b/arch/x86/platform/efi/efi_64.c
> > @@ -47,16 +47,7 @@
> > */
> > static u64 efi_va = EFI_VA_START;
> >
> > -/*
> > - * Scratch space used for switching the pagetable in the EFI stub
> > - */
> > -struct efi_scratch {
> > - u64 r15;
> > - u64 prev_cr3;
> > - pgd_t *efi_pgt;
> > - bool use_pgd;
> > - u64 phys_stack;
> > -} __packed;
> > +struct efi_scratch efi_scratch;
> >
> > static void __init early_code_mapping_set_exec(int executable)
> > {
> > @@ -83,8 +74,11 @@ pgd_t * __init efi_call_phys_prolog(void)
> > int pgd;
> > int n_pgds;
> >
> > - if (!efi_enabled(EFI_OLD_MEMMAP))
> > - return NULL;
> > + if (!efi_enabled(EFI_OLD_MEMMAP)) {
> > + save_pgd = (pgd_t *)read_cr3();
> > + write_cr3((unsigned long)efi_scratch.efi_pgt);
> > + goto out;
> > + }
> >
> > early_code_mapping_set_exec(1);
> >
> > @@ -96,6 +90,7 @@ pgd_t * __init efi_call_phys_prolog(void)
> > vaddress = (unsigned long)__va(pgd * PGDIR_SIZE);
> > set_pgd(pgd_offset_k(pgd * PGDIR_SIZE), *pgd_offset_k(vaddress));
> > }
> > +out:
> > __flush_tlb_all();
> >
> > return save_pgd;
> > @@ -109,8 +104,11 @@ void __init efi_call_phys_epilog(pgd_t *save_pgd)
>
> There's a comment here:
>
> /*
> * After the lock is released, the original page table is restored.
> */
>
> Which lock are we talking about?

No idea, we don't take any locks. Looks like a stale comment.