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    Subject[tip:x86/pti] x86/pgtable/32: Allocate 8k page-tables when PTI is enabled
    Commit-ID:  e3238faf20fb1b51a814497751398ab525a2c884
    Gitweb: https://git.kernel.org/tip/e3238faf20fb1b51a814497751398ab525a2c884
    Author: Joerg Roedel <jroedel@suse.de>
    AuthorDate: Wed, 18 Jul 2018 11:40:54 +0200
    Committer: Thomas Gleixner <tglx@linutronix.de>
    CommitDate: Fri, 20 Jul 2018 01:11:41 +0200

    x86/pgtable/32: Allocate 8k page-tables when PTI is enabled

    Allocate a kernel and a user page-table root when PTI is enabled. Also
    allocate a full page per root for PAE because otherwise the bit to flip in
    CR3 to switch between them would be non-constant, which creates a lot of
    hassle. Keep that for a later optimization.

    Signed-off-by: Joerg Roedel <jroedel@suse.de>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Tested-by: Pavel Machek <pavel@ucw.cz>
    Cc: "H . Peter Anvin" <hpa@zytor.com>
    Cc: linux-mm@kvack.org
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Dave Hansen <dave.hansen@intel.com>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Juergen Gross <jgross@suse.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Jiri Kosina <jkosina@suse.cz>
    Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
    Cc: Brian Gerst <brgerst@gmail.com>
    Cc: David Laight <David.Laight@aculab.com>
    Cc: Denys Vlasenko <dvlasenk@redhat.com>
    Cc: Eduardo Valentin <eduval@amazon.com>
    Cc: Greg KH <gregkh@linuxfoundation.org>
    Cc: Will Deacon <will.deacon@arm.com>
    Cc: aliguori@amazon.com
    Cc: daniel.gruss@iaik.tugraz.at
    Cc: hughd@google.com
    Cc: keescook@google.com
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: Waiman Long <llong@redhat.com>
    Cc: "David H . Gutteridge" <dhgutteridge@sympatico.ca>
    Cc: joro@8bytes.org
    Link: https://lkml.kernel.org/r/1531906876-13451-18-git-send-email-joro@8bytes.org

    ---
    arch/x86/kernel/head_32.S | 20 +++++++++++++++-----
    arch/x86/mm/pgtable.c | 5 +++--
    2 files changed, 18 insertions(+), 7 deletions(-)

    diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
    index abe6df15a8fb..30f9cb2c0b55 100644
    --- a/arch/x86/kernel/head_32.S
    +++ b/arch/x86/kernel/head_32.S
    @@ -512,11 +512,18 @@ ENTRY(initial_code)
    ENTRY(setup_once_ref)
    .long setup_once

    +#ifdef CONFIG_PAGE_TABLE_ISOLATION
    +#define PGD_ALIGN (2 * PAGE_SIZE)
    +#define PTI_USER_PGD_FILL 1024
    +#else
    +#define PGD_ALIGN (PAGE_SIZE)
    +#define PTI_USER_PGD_FILL 0
    +#endif
    /*
    * BSS section
    */
    __PAGE_ALIGNED_BSS
    - .align PAGE_SIZE
    + .align PGD_ALIGN
    #ifdef CONFIG_X86_PAE
    .globl initial_pg_pmd
    initial_pg_pmd:
    @@ -526,14 +533,17 @@ initial_pg_pmd:
    initial_page_table:
    .fill 1024,4,0
    #endif
    + .align PGD_ALIGN
    initial_pg_fixmap:
    .fill 1024,4,0
    -.globl empty_zero_page
    -empty_zero_page:
    - .fill 4096,1,0
    .globl swapper_pg_dir
    + .align PGD_ALIGN
    swapper_pg_dir:
    .fill 1024,4,0
    + .fill PTI_USER_PGD_FILL,4,0
    +.globl empty_zero_page
    +empty_zero_page:
    + .fill 4096,1,0
    EXPORT_SYMBOL(empty_zero_page)

    /*
    @@ -542,7 +552,7 @@ EXPORT_SYMBOL(empty_zero_page)
    #ifdef CONFIG_X86_PAE
    __PAGE_ALIGNED_DATA
    /* Page-aligned for the benefit of paravirt? */
    - .align PAGE_SIZE
    + .align PGD_ALIGN
    ENTRY(initial_page_table)
    .long pa(initial_pg_pmd+PGD_IDENT_ATTR),0 /* low identity map */
    # if KPMDS == 3
    diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
    index 47b5951e592b..db6fb7740bf7 100644
    --- a/arch/x86/mm/pgtable.c
    +++ b/arch/x86/mm/pgtable.c
    @@ -343,7 +343,8 @@ static inline pgd_t *_pgd_alloc(void)
    * We allocate one page for pgd.
    */
    if (!SHARED_KERNEL_PMD)
    - return (pgd_t *)__get_free_page(PGALLOC_GFP);
    + return (pgd_t *)__get_free_pages(PGALLOC_GFP,
    + PGD_ALLOCATION_ORDER);

    /*
    * Now PAE kernel is not running as a Xen domain. We can allocate
    @@ -355,7 +356,7 @@ static inline pgd_t *_pgd_alloc(void)
    static inline void _pgd_free(pgd_t *pgd)
    {
    if (!SHARED_KERNEL_PMD)
    - free_page((unsigned long)pgd);
    + free_pages((unsigned long)pgd, PGD_ALLOCATION_ORDER);
    else
    kmem_cache_free(pgd_cache, pgd);
    }
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