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Date: Sun, 26 Nov 2017 16:15:02 +0100 From: Ingo Molnar <mingo@...nel.org> To: Peter Zijlstra <peterz@...radead.org> Cc: linux-kernel@...r.kernel.org, Dave Hansen <dave.hansen@...ux.intel.com>, Andy Lutomirski <luto@...capital.net>, Thomas Gleixner <tglx@...utronix.de>, "H . Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>, Linus Torvalds <torvalds@...ux-foundation.org> Subject: Re: [PATCH 25/43] x86/mm/kaiser: Unmap kernel from userspace page tables (core patch) * Peter Zijlstra <peterz@...radead.org> wrote: > On Fri, Nov 24, 2017 at 10:14:30AM +0100, Ingo Molnar wrote: > > +static pte_t *kaiser_shadow_pagetable_walk(unsigned long address, > > + unsigned long flags) > > +{ > > + pte_t *pte; > > + pmd_t *pmd; > > + pud_t *pud; > > + p4d_t *p4d; > > + pgd_t *pgd = kernel_to_shadow_pgdp(pgd_offset_k(address)); > > + gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO); > > + > > + if (flags & KAISER_WALK_ATOMIC) { > > + gfp &= ~GFP_KERNEL; > > + gfp |= __GFP_HIGH | __GFP_ATOMIC; > > + } > > + > > + if (address < PAGE_OFFSET) { > > + WARN_ONCE(1, "attempt to walk user address\n"); > > + return NULL; > > + } > > + > > + if (pgd_none(*pgd)) { > > + WARN_ONCE(1, "All shadow pgds should have been populated\n"); > > + return NULL; > > + } > > + BUILD_BUG_ON(pgd_large(*pgd) != 0); > > + > > + p4d = p4d_offset(pgd, address); > > + BUILD_BUG_ON(p4d_large(*p4d) != 0); > > + if (p4d_none(*p4d)) { > > + unsigned long new_pud_page = __get_free_page(gfp); > > + if (!new_pud_page) > > + return NULL; > > + > > + spin_lock(&shadow_table_allocation_lock); > > + if (p4d_none(*p4d)) > > + set_p4d(p4d, __p4d(_KERNPG_TABLE | __pa(new_pud_page))); > > + else > > + free_page(new_pud_page); > > + spin_unlock(&shadow_table_allocation_lock); > > So mm/memory.c has two patterns here.. I prefer the other one: > > spin_lock(&shadow_table_allocation_lock); > if (p4d_none(*p4d)) { > set_p4d(p4d, __p4d(_KERNEL_TABLE | __pa(new_pud_page))); > new_pud_page = NULL; > } > spin_unlock(&shadow_table_allocation_lock); > if (new_pud_page) > free_page(new_pud_page); > > > + } Ok, would be nice to get this cleanup as a delta patch, because the existing pattern has been tested to a fair degree already. Thanks, Ingo
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