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x86/mm/pti: Remove dead logic in pti_user_pagetable_walk*()
The following code contains dead logic:
162 if (pgd_none(*pgd)) {
163 unsigned long new_p4d_page = __get_free_page(gfp);
164 if (!new_p4d_page)
165 return NULL;
166
167 if (pgd_none(*pgd)) {
168 set_pgd(pgd, __pgd(_KERNPG_TABLE | __pa(new_p4d_page)));
169 new_p4d_page = 0;
170 }
171 if (new_p4d_page)
172 free_page(new_p4d_page);
173 }
There can't be any difference between two pgd_none(*pgd) at L162 and L167,
so it's always false at L171.
Dave Hansen explained:
Yes, the double-test was part of an optimization where we attempted to
avoid using a global spinlock in the fork() path. We would check for
unallocated mid-level page tables without the lock. The lock was only
taken when we needed to *make* an entry to avoid collisions.
Now that it is all single-threaded, there is no chance of a collision,
no need for a lock, and no need for the re-check.
As all these functions are only called during init, mark them __init as
well.
Fixes: 03f4424f34
("x86/mm/pti: Add functions to clone kernel PMDs")
Signed-off-by: Jike Song <albcamus@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Alan Cox <gnomes@lxorguk.ukuu.org.uk>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Jiri Koshina <jikos@kernel.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Kees Cook <keescook@google.com>
Cc: Andi Lutomirski <luto@amacapital.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Greg KH <gregkh@linux-foundation.org>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: Paul Turner <pjt@google.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20180108160341.3461-1-albcamus@gmail.com
This commit is contained in:
parent
262b6b3008
commit
8d56eff266
1 changed files with 6 additions and 26 deletions
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@ -149,7 +149,7 @@ pgd_t __pti_set_user_pgd(pgd_t *pgdp, pgd_t pgd)
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*
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* Returns a pointer to a P4D on success, or NULL on failure.
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*/
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static p4d_t *pti_user_pagetable_walk_p4d(unsigned long address)
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static __init p4d_t *pti_user_pagetable_walk_p4d(unsigned long address)
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{
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pgd_t *pgd = kernel_to_user_pgdp(pgd_offset_k(address));
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gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO);
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@ -164,12 +164,7 @@ static p4d_t *pti_user_pagetable_walk_p4d(unsigned long address)
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if (!new_p4d_page)
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return NULL;
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if (pgd_none(*pgd)) {
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set_pgd(pgd, __pgd(_KERNPG_TABLE | __pa(new_p4d_page)));
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new_p4d_page = 0;
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}
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if (new_p4d_page)
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free_page(new_p4d_page);
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set_pgd(pgd, __pgd(_KERNPG_TABLE | __pa(new_p4d_page)));
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}
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BUILD_BUG_ON(pgd_large(*pgd) != 0);
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@ -182,7 +177,7 @@ static p4d_t *pti_user_pagetable_walk_p4d(unsigned long address)
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*
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* Returns a pointer to a PMD on success, or NULL on failure.
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*/
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static pmd_t *pti_user_pagetable_walk_pmd(unsigned long address)
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static __init pmd_t *pti_user_pagetable_walk_pmd(unsigned long address)
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{
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gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO);
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p4d_t *p4d = pti_user_pagetable_walk_p4d(address);
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@ -194,12 +189,7 @@ static pmd_t *pti_user_pagetable_walk_pmd(unsigned long address)
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if (!new_pud_page)
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return NULL;
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if (p4d_none(*p4d)) {
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set_p4d(p4d, __p4d(_KERNPG_TABLE | __pa(new_pud_page)));
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new_pud_page = 0;
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}
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if (new_pud_page)
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free_page(new_pud_page);
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set_p4d(p4d, __p4d(_KERNPG_TABLE | __pa(new_pud_page)));
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}
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pud = pud_offset(p4d, address);
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@ -213,12 +203,7 @@ static pmd_t *pti_user_pagetable_walk_pmd(unsigned long address)
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if (!new_pmd_page)
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return NULL;
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if (pud_none(*pud)) {
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set_pud(pud, __pud(_KERNPG_TABLE | __pa(new_pmd_page)));
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new_pmd_page = 0;
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}
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if (new_pmd_page)
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free_page(new_pmd_page);
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set_pud(pud, __pud(_KERNPG_TABLE | __pa(new_pmd_page)));
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}
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return pmd_offset(pud, address);
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@ -251,12 +236,7 @@ static __init pte_t *pti_user_pagetable_walk_pte(unsigned long address)
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if (!new_pte_page)
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return NULL;
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if (pmd_none(*pmd)) {
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set_pmd(pmd, __pmd(_KERNPG_TABLE | __pa(new_pte_page)));
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new_pte_page = 0;
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}
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if (new_pte_page)
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free_page(new_pte_page);
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set_pmd(pmd, __pmd(_KERNPG_TABLE | __pa(new_pte_page)));
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}
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pte = pte_offset_kernel(pmd, address);
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