On 4/28/22 16:44, Kai Huang wrote: >> Just like the SME test, it doesn't even need to be precise. It just >> needs to be 100% accurate in that it is *ALWAYS* set for any system that >> might have dirtied cache aliases. >> >> I'm not sure why you are so fixated on SEAMRR specifically for this. > I see. I think I can simply use MTRR.SEAMRR bit check. If CPU supports SEAMRR, > then basically it supports MKTME. > > Is this look good for you? Sure, fine, as long as it comes with a coherent description that explains why the check is good enough. >>> "During initializing the TDX module, one step requires some SEAMCALL must be >>> done on all logical cpus enabled by BIOS, otherwise a later step will fail. >>> Disable CPU hotplug during the initialization process to prevent any CPU going >>> offline during initializing the TDX module. Note it is caller's responsibility >>> to guarantee all BIOS-enabled CPUs are in cpu_present_mask and all present CPUs >>> are online." >> But, what if a CPU went offline just before this lock was taken? What >> if the caller make sure all present CPUs are online, makes the call, >> then a CPU is taken offline. The lock wouldn't do any good. >> >> What purpose does the lock serve? > I thought cpus_read_lock() can prevent any CPU from going offline, no? It doesn't prevent squat before the lock is taken, though.
