终于好了。原来我在kernel编译时选择了下面这些：
Device Drivers --->ATA/ATAPI/MFM/RLL support --->
[*] Support for SATA (deprecated; conflicts with libata SATA driver)
Device Drivers --->SCSI device support ---> SCSI low-level drivers --->
[*] Serial ATA (SATA) support
<*> Intel PIIX/ICH SATA support
呜~，它都说conficts了，我还选……
后来把Support for SATA去掉后就快了，用/dev/sda?访问