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Commit ce0fa3e5 authored by Tony Luck's avatar Tony Luck Committed by Ingo Molnar
Browse files

x86/mm, mm/hwpoison: Clear PRESENT bit for kernel 1:1 mappings of poison pages 

Speculative processor accesses may reference any memory that has a
valid page table entry.  While a speculative access won't generate
a machine check, it will log the error in a machine check bank. That
could cause escalation of a subsequent error since the overflow bit
will be then set in the machine check bank status register.

Code has to be double-plus-tricky to avoid mentioning the 1:1 virtual
address of the page we want to map out otherwise we may trigger the
very problem we are trying to avoid.  We use a non-canonical address
that passes through the usual Linux table walking code to get to the
same "pte".

Thanks to Dave Hansen for reviewing several iterations of this.

Also see:

  http://marc.info/?l=linux-mm&m=149860136413338&w=2



Signed-off-by: default avatarTony Luck <tony.luck@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Elliott, Robert (Persistent Memory) <elliott@hpe.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mm@kvack.org
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/20170816171803.28342-1-tony.luck@intel.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 57bd1905

arch/x86/include/asm/page_64.h

+4 −0
Original line number Original line Diff line number Diff line
@@ -51,6 +51,10 @@ static inline void clear_page(void *page) 




void copy_page(void *to, void *from);

void copy_page(void *to, void *from);





#ifdef CONFIG_X86_MCE

#define arch_unmap_kpfn arch_unmap_kpfn

#endif



#endif	/* !__ASSEMBLY__ */

#endif	/* !__ASSEMBLY__ */





#ifdef CONFIG_X86_VSYSCALL_EMULATION

#ifdef CONFIG_X86_VSYSCALL_EMULATION

arch/x86/kernel/cpu/mcheck/mce.c

+43 −0
Original line number Original line Diff line number Diff line
@@ -51,6 +51,7 @@ 
#include <asm/mce.h>

#include <asm/mce.h>

#include <asm/msr.h>

#include <asm/msr.h>

#include <asm/reboot.h>

#include <asm/reboot.h>

#include <asm/set_memory.h>





#include "mce-internal.h"

#include "mce-internal.h"
@@ -1051,6 +1052,48 @@ static int do_memory_failure(struct mce *m) 
	return ret;

	return ret;

}

}





#if defined(arch_unmap_kpfn) && defined(CONFIG_MEMORY_FAILURE)



void arch_unmap_kpfn(unsigned long pfn)

{

	unsigned long decoy_addr;



	/*

	 * Unmap this page from the kernel 1:1 mappings to make sure

	 * we don't log more errors because of speculative access to

	 * the page.

	 * We would like to just call:

	 *	set_memory_np((unsigned long)pfn_to_kaddr(pfn), 1);

	 * but doing that would radically increase the odds of a

	 * speculative access to the posion page because we'd have

	 * the virtual address of the kernel 1:1 mapping sitting

	 * around in registers.

	 * Instead we get tricky.  We create a non-canonical address

	 * that looks just like the one we want, but has bit 63 flipped.

	 * This relies on set_memory_np() not checking whether we passed

	 * a legal address.

	 */



/*

 * Build time check to see if we have a spare virtual bit. Don't want

 * to leave this until run time because most developers don't have a

 * system that can exercise this code path. This will only become a

 * problem if/when we move beyond 5-level page tables.

 *

 * Hard code "9" here because cpp doesn't grok ilog2(PTRS_PER_PGD)

 */

#if PGDIR_SHIFT + 9 < 63

	decoy_addr = (pfn << PAGE_SHIFT) + (PAGE_OFFSET ^ BIT(63));

#else

#error "no unused virtual bit available"

#endif



	if (set_memory_np(decoy_addr, 1))

		pr_warn("Could not invalidate pfn=0x%lx from 1:1 map\n", pfn);



}

#endif



/*

/*

 * The actual machine check handler. This only handles real

 * The actual machine check handler. This only handles real

 * exceptions when something got corrupted coming in through int 18.

 * exceptions when something got corrupted coming in through int 18.

include/linux/mm_inline.h

+6 −0
Original line number Original line Diff line number Diff line
@@ -126,4 +126,10 @@ static __always_inline enum lru_list page_lru(struct page *page) 




#define lru_to_page(head) (list_entry((head)->prev, struct page, lru))

#define lru_to_page(head) (list_entry((head)->prev, struct page, lru))





#ifdef arch_unmap_kpfn

extern void arch_unmap_kpfn(unsigned long pfn);

#else

static __always_inline void arch_unmap_kpfn(unsigned long pfn) { }

#endif



#endif
 
#endif

mm/memory-failure.c

+2 −0
Original line number Original line Diff line number Diff line
@@ -1146,6 +1146,8 @@ int memory_failure(unsigned long pfn, int trapno, int flags) 
		return 0;

		return 0;

	}

	}





	arch_unmap_kpfn(pfn);



	orig_head = hpage = compound_head(p);

	orig_head = hpage = compound_head(p);

	num_poisoned_pages_inc();

	num_poisoned_pages_inc();