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SubjectRe: v4.4-rc8 based tip tree kernel hangs on boot.
On Tue, 19 Jan, at 04:17:15PM, Srikar Dronamraju wrote:
> * Matt Fleming <matt@codeblueprint.co.uk> [2016-01-18 15:40:01]:
>
> > On Sun, 17 Jan, at 11:02:48PM, Srikar Dronamraju wrote:
> > >
> > > Unfortunately even with your below patch on top of c9f2a9a ("x86/efi:
> > > Hoist page table switching code into efi_call_virt()" also fails to boot
> > > with and without CONFIG_DEBUG_WX=y. I have added CONFIG_EFI_PGT_DUMP.
> >
> > What about if you comment out the call to efi_dump_pagetable()? What
> > if you return early from efi_sync_low_kernel_mappings(), e.g.
>
> This doesnt help but ....
>
> >
> > diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
> > index 71121a9d06cf..e1f8ebb88f84 100644
> > --- a/arch/x86/platform/efi/efi_64.c
> > +++ b/arch/x86/platform/efi/efi_64.c
> > @@ -177,6 +177,8 @@ void efi_sync_low_kernel_mappings(void)
> > init_mm.pgd + pgd_index(PAGE_OFFSET),
> > sizeof(pgd_t) * num_pgds);
> >
> > + return;
> > +
>
> This alone makes it boot. dmesg below
>
> i.e git checkout tip/x86/efi
> +
> git am <your patch> + <the above fixlet>
>

OK could you add efi=debug to your kernel cmdline and try this patch
instead of the one that returns early from
efi_sync_low_kernel_mappings()?

I also pushed out all the changes to the following branch if that's
easier to pull and build,

https://git.kernel.org/cgit/linux/kernel/git/mfleming/efi.git/log/?h=bug/efi/srikar

I have no idea why any of these entries would be empty, but this is
the only thing I can imagine could go wrong with this code,

diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index 71121a9d06cf..9b610aa17683 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -192,6 +192,9 @@ void efi_sync_low_kernel_mappings(void)
pgd_efi = efi_pgd + pgd_index(PAGE_OFFSET);
pgd_k = pgd_offset_k(PAGE_OFFSET);

+ if (WARN_ON_ONCE(pgd_none(*pgd_efi) || pgd_none(*pgd_k)))
+ return;
+
num_entries = pgd_index(EFI_VA_END) - pgd_index(PAGE_OFFSET);
memcpy(pgd_efi, pgd_k, sizeof(pgd_t) * num_entries);

@@ -203,17 +206,26 @@ void efi_sync_low_kernel_mappings(void)
BUILD_BUG_ON((EFI_VA_END & ~PUD_MASK) != 0);

pgd_efi = efi_pgd + pgd_index(EFI_VA_END);
- pud_efi = pud_offset(pgd_efi, 0);
-
pgd_k = pgd_offset_k(EFI_VA_END);
+
+ if (WARN_ON_ONCE(pgd_none(*pgd_efi) || pgd_none(*pgd_k)))
+ return;
+
+ pud_efi = pud_offset(pgd_efi, 0);
pud_k = pud_offset(pgd_k, 0);

+ if (WARN_ON_ONCE(pud_none(*pud_efi) || pud_none(*pud_k)))
+ return;
+
num_entries = pud_index(EFI_VA_END);
memcpy(pud_efi, pud_k, sizeof(pud_t) * num_entries);

pud_efi = pud_offset(pgd_efi, EFI_VA_START);
pud_k = pud_offset(pgd_k, EFI_VA_START);

+ if (WARN_ON_ONCE(pud_none(*pud_efi) || pud_none(*pud_k)))
+ return;
+
num_entries = PTRS_PER_PUD - pud_index(EFI_VA_START);
memcpy(pud_efi, pud_k, sizeof(pud_t) * num_entries);
}

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