linux-kernel - Re: [PATCH 4.9] x86/pti/efi: broken conversion from efi to kernel page table

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Date:   Sat, 13 Jan 2018 12:40:10 -0500
From:   Pavel Tatashin <pasha.tatashin@...cle.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Steve Sistare <steven.sistare@...cle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>, mingo@...hat.com,
        hpa@...or.com, x86@...nel.org, Jiri Kosina <jkosina@...e.cz>,
        Hugh Dickins <hughd@...gle.com>, dave.hansen@...ux.intel.com,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 4.9] x86/pti/efi: broken conversion from efi to kernel
 page table

Hi Greg,

Yeah, the one in pgtable.c needs to be removed, I wonder how it
compiled... I will submit a new patch for 4.9 sometime later.

Thank you,
Pavel

On Sat, Jan 13, 2018 at 12:12 PM, Greg KH <gregkh@...uxfoundation.org> wrote:
> On Thu, Jan 11, 2018 at 04:58:20PM -0500, Pavel Tatashin wrote:
>> The page table order must be increased for EFI table in order to avoid a
>> bug where NMI tries to change the page table to kernel page table, while
>> efi page table is active.
>>
>> For more disccussion about this bug, see this thread:
>> http://lkml.iu.edu/hypermail/linux/kernel/1801.1/00951.html
>>
>> Signed-off-by: Pavel Tatashin <pasha.tatashin@...cle.com>
>> Reviewed-by: Steven Sistare <steven.sistare@...cle.com>
>> Acked-by: Jiri Kosina <jkosina@...e.cz>
>> ---
>>  arch/x86/include/asm/pgalloc.h | 11 +++++++++++
>>  arch/x86/platform/efi/efi_64.c |  2 +-
>>  2 files changed, 12 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/include/asm/pgalloc.h b/arch/x86/include/asm/pgalloc.h
>> index b6d425999f99..1178a51b77f3 100644
>> --- a/arch/x86/include/asm/pgalloc.h
>> +++ b/arch/x86/include/asm/pgalloc.h
>> @@ -27,6 +27,17 @@ static inline void paravirt_release_pud(unsigned long pfn) {}
>>   */
>>  extern gfp_t __userpte_alloc_gfp;
>>
>> +#ifdef CONFIG_PAGE_TABLE_ISOLATION
>> +/*
>> + * Instead of one PGD, we acquire two PGDs.  Being order-1, it is
>> + * both 8k in size and 8k-aligned.  That lets us just flip bit 12
>> + * in a pointer to swap between the two 4k halves.
>> + */
>> +#define PGD_ALLOCATION_ORDER 1
>> +#else
>> +#define PGD_ALLOCATION_ORDER 0
>> +#endif
>
> This conflicts with the definition of PGD_ALLOCATION_ORDER in
> arch/x86/mm/pgtable.c that says:
>
> /*
>  * Instead of one pgd, Kaiser acquires two pgds.  Being order-1, it is
>  * both 8k in size and 8k-aligned.  That lets us just flip bit 12
>  * in a pointer to swap between the two 4k halves.
>  */
> #define PGD_ALLOCATION_ORDER    kaiser_enabled
>
> So, which is it?
>
> I'm going to go drop this from the 4.9 stable queue because of this.
>
> thanks,
>
> greg k-h