commit e1557fbc4ed4ca063b79a1820f7cb8778ed210ed
parent 38330b1aafc83946ee301b9f4f74f4babeb8982a
Author: Brian Swetland <swetland@frotz.net>
Date: Tue, 31 Dec 2013 09:18:28 -0800
update notes, add comments on vm arrangement
Diffstat:
1 file changed, 16 insertions(+), 2 deletions(-)
diff --git a/README.64BIT b/README.64BIT
@@ -24,6 +24,8 @@ DONE
* implement a 32bit multiboot header and shim
* setup an initial identity-mapped and kernel-address-mapped
pagetable since you cannot enter 64bit mode without paging on
+ * adjust syscall assembly for 64bit
+ * implement 64bit task switch glue
IN PROGRESS
* introduce new type (currently 'uintp' for unsigned integer the size
@@ -37,9 +39,7 @@ IN PROGRESS
TODO
* implement 64bit GDT and TSS setup
* implement 64bit interrupt support and IDT setup
- * implement 64bit task switch glue
* adjust process entry code for 64bit
- * adjust syscall assembly for 64bit
* verify usermode works
* verify usertests work
* update boot sector to support multiboot extended header
@@ -63,10 +63,24 @@ LESSONS LEARNED / UNRESOLVED
for page tables.
* Xv6:32's trick for cpu-local storage does not work on gcc x86-64
- see README.CLS for an exploration of alternate options
+ * Not sure why you're double/triple-faulting?
+ drop some instrumentation code in qemu/target-i386/seg_helper.c's
+ do_interrupt64() -- this is where all the validation on irq/trap
+ entry happens
IMPLEMENTATION NOTES
* use "kernel" addressing mode for kernel compilation
* kernel virtual address space 0xFFFFFFFF80000000:0xFFFFFFFFFF000000
* linear-map first 1GB of RAM to kernel virtual address space
* linear-map first 1GB of RAM 1:1 during boot
+ * x64 has 4 levels of page tables instead of just 2
+ * continue to return a 2nd-level page table from setupkvm()
+ but actually create 4th, 3rd, and 2nd level tables
+ * use the top two entries of the 2nd level table for backpointers
+ to the 4th and 3rd level tables so that switchkvm(), switchuvm(),
+ and freevm() can get at these when needed
+ * use the top entry of the 4th level table to point to a shared
+ (among all processes) 3rd level table which handles the kernel
+ memory mapping (which is the same everywhere)
+ * userland will have 4GB - 8KB address space
