Hi, Would like to discuss virt_to_phys() and phys_to_virt() conversion in latest kernel. I can see that if VA < PAGE_OFFSET, then we just subtract kimage_voffset from VA and we get the PA. However, there is no such condition for phys_to_virt(). phys_to_virt is always done by (PA - PHYS_OFFSET + PAGE_OFFSET). So, how does phys_to_virt() work for all the cases? I must be missing something. -- I am using a platform with VA bits = 42. Therefore PAGE_OFFSET on my platform is 0xfffffe0000000000 PHYS_OFFSET is 0x8000000000 kimage_voffset is 0xfffffb8006000000 Now lets find physical address of log_buf: # cat /proc/kallsyms | grep -w "d log_buf" fffffc0008ca6b40 d log_buf Since VA < PAGE_OFFSET (fffffc0008ca6b40 < fffffe0000000000) Therefore as per definition of virt_to_phys() from asm/memory.h: PA = VA - kimage_voffset = fffffc0008ca6b40 - fffffb8006000000 = 8002CA6B40 Now convert PA=8002CA6B40 to VA. VA = PA - PHYS_OFFSET + PAGE_OFFSET = 8002CA6B40 - 8000000000 + fffffe0000000000 = fffffe0002CA6B40 which not equal to fffffc0008ca6b40. So, do we have dual mapping for all physical addresses? If not, how does it work? What I am missing. If its dual mapping, then probably we will need to fix couple of things in kexec-tools. ~Pratyush
