On Tue, Dec 15, 2015 at 5:11 AM, Borislav Petkov <bp@xxxxxxxxx> wrote: > On Thu, Dec 10, 2015 at 04:21:50PM -0800, Tony Luck wrote: >> Using __copy_user_nocache() as inspiration create a memory copy >> routine for use by kernel code with annotations to allow for >> recovery from machine checks. >> >> Notes: >> 1) Unlike the original we make no attempt to copy all the bytes >> up to the faulting address. The original achieves that by >> re-executing the failing part as a byte-by-byte copy, >> which will take another page fault. We don't want to have >> a second machine check! >> 2) Likewise the return value for the original indicates exactly >> how many bytes were not copied. Instead we provide the physical >> address of the fault (thanks to help from do_machine_check() >> 3) Provide helpful macros to decode the return value. >> >> Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx> >> --- >> arch/x86/include/asm/uaccess_64.h | 5 +++ >> arch/x86/kernel/x8664_ksyms_64.c | 2 + >> arch/x86/lib/copy_user_64.S | 91 +++++++++++++++++++++++++++++++++++++++ >> 3 files changed, 98 insertions(+) > > ... > >> + * mcsafe_memcpy - Uncached memory copy with machine check exception handling >> + * Note that we only catch machine checks when reading the source addresses. >> + * Writes to target are posted and don't generate machine checks. >> + * This will force destination/source out of cache for more performance. > > ... and the non-temporal version is the optimal one even though we're > defaulting to copy_user_enhanced_fast_string for memcpy on modern Intel > CPUs...? At least the pmem driver use case does not want caching of the source-buffer since that is the raw "disk" media. I.e. in pmem_do_bvec() we'd use this to implement memcpy_from_pmem(). However, caching the destination-buffer may prove beneficial since that data is likely to be consumed immediately by the thread that submitted the i/o. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>