From: David Laight > Sent: 18 April 2019 10:21 > From: Fenghua Yu > > Sent: 17 April 2019 22:34 > > > > set_cpu_cap() calls locked BTS and clear_cpu_cap() calls locked BTR to > > operate on bitmap defined in x86_capability. > > > > Locked BTS/BTR accesses a single unsigned long location. In 64-bit mode, > > the location is at: > > base address of x86_capability + (bit offset in x86_capability / 64) * 8 > > > > Since base address of x86_capability may not be aligned to unsigned long, > > the single unsigned long location may cross two cache lines and > > accessing the location by locked BTS/BTR introductions will cause > > split lock. > > Isn't the problem that the type (and definition) of x86_capability[] are wrong. > If the 'bitmap' functions are used for it, it should be defined as a bitmap. > This would make it 'unsigned long' not __u32. > > This type munging of bitmaps only works on LE systems. > > OTOH the locked BTS/BTR instructions could be changed to use 32 bit accesses. > ISTR some of the associated functions use byte accesses. > > Perhaps there ought to be asm wrappers for BTS/BTR that do 8bit and > 32bit accesses. A quick look shows that this isn't the only __32[] that is being cast to (unsigned long) and then to set/test/clear_bit() in those files. I wonder how much other code is applying such casts? David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
