[patch][rfc] Larger IO bitmap

[Stas Sergeev]

Hello.

This topic was already discussed many times
on that list and it seems there was not too
much opposition to enlarging the IO bitmap.

The previous discussion was started here:
http://www.uwsg.iu.edu/hypermail/linux/kernel/0211.0/0477.html
but in 2.4 times this was kind of problematic.

Now, with the lazy bitmap allocation and
per-CPU TSS, this will really not drain any
resources I think. 8K TSS increase and 8K
per process *that does ioperm()* - I think
it is not very bad.
The reasons why I need that, are described
in the URL above. Basically this will
allow to use full-screen VESA under dosemu
(without LFB though), and this may be also
helpfull for the XFree project and some
other projects:
http://www.uwsg.iu.edu/hypermail/linux/kernel/9807.1/1079.html

I made the patch, it seems to work well.
It is attached. I am wondering are there
any chances to ever get that in? Or why
not? It can also be made as a config
option, but taking the lazy allocation
into account, I think this is not really
necessary. But I can do that if needed.

So would it be possible to ever have the
full IO bitmap under linux, or the current
solution is permanent?

--- linux/include/asm-i386/desc.h	2004-01-09 09:59:02.000000000 +0300
+++ linux/include/asm-i386/desc.h	2004-03-15 12:35:33.000000000 +0300
@@ -44,7 +44,8 @@
 
 static inline void __set_tss_desc(unsigned int cpu, unsigned int entry, void *addr)
 {
-	_set_tssldt_desc(&cpu_gdt_table[cpu][entry], (int)addr, 235, 0x89);
+	_set_tssldt_desc(&cpu_gdt_table[cpu][entry], (int)addr,
+		offsetof(struct tss_struct, __cacheline_filler) - 1, 0x89);
 }
 
 #define set_tss_desc(cpu,addr) __set_tss_desc(cpu, GDT_ENTRY_TSS, addr)
--- linux/include/asm-i386/processor.h	2004-01-09 09:59:06.000000000 +0300
+++ linux/include/asm-i386/processor.h	2004-03-15 13:51:13.317081840 +0300
@@ -302,9 +302,9 @@
 #define TASK_UNMAPPED_BASE	(PAGE_ALIGN(TASK_SIZE / 3))
 
 /*
- * Size of io_bitmap, covering ports 0 to 0x3ff.
+ * Size of io_bitmap.
  */
-#define IO_BITMAP_BITS  1024
+#define IO_BITMAP_BITS  65536
 #define IO_BITMAP_BYTES (IO_BITMAP_BITS/8)
 #define IO_BITMAP_LONGS (IO_BITMAP_BYTES/sizeof(long))
 #define IO_BITMAP_OFFSET offsetof(struct tss_struct,io_bitmap)
@@ -396,7 +396,7 @@
 	/*
 	 * pads the TSS to be cacheline-aligned (size is 0x100)
 	 */
-	unsigned long __cacheline_filler[5];
+	unsigned long __cacheline_filler[37];
 	/*
 	 * .. and then another 0x100 bytes for emergency kernel stack
 	 */
--- linux/include/asm-mips/processor.h	2004-01-09 09:59:05.000000000 +0300
+++ linux/include/asm-mips/processor.h	2004-03-15 13:47:05.602740144 +0300
@@ -172,9 +172,9 @@
 #endif
 
 /*
- * Size of io_bitmap in longwords: 32 is ports 0-0x3ff.
+ * Size of io_bitmap in longwords.
  */
-#define IO_BITMAP_SIZE	32
+#define IO_BITMAP_SIZE	2048
 
 #define NUM_FPU_REGS	32
 
--- linux/include/asm-i386_64/processor.h	2004-02-02 13:22:51.000000000 +0300
+++ linux/include/asm-i386_64/processor.h	2004-03-15 13:47:46.174572288 +0300
@@ -179,9 +179,9 @@
 	(test_thread_flag(TIF_IA32) ? TASK_UNMAPPED_32 : TASK_UNMAPPED_64)  
 
 /*
- * Size of io_bitmap, covering ports 0 to 0x3ff.
+ * Size of io_bitmap.
  */
-#define IO_BITMAP_BITS  1024
+#define IO_BITMAP_BITS  65536
 #define IO_BITMAP_BYTES (IO_BITMAP_BITS/8)
 #define IO_BITMAP_LONGS (IO_BITMAP_BYTES/sizeof(long))
 #define IO_BITMAP_OFFSET offsetof(struct tss_struct,io_bitmap)

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