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Subject[PATCH] x86/iopl: Clear up the role of the two bitmap copying fields

Here's another one, which makes the pointer-caching logic a bit clearer
IMO:

Firstly, it lines up the two related fields in the namespace:

x86_io_bitmap.last_bitmap => bitmap_copied_ptr
x86_io_bitmap.last_sequence => bitmap_copied_seq

It also constifies the pointer to better signal that it should never
actually be used for anything but comparison

I think the 'bitmap_copied_' ptr/seq pairing makes it more obvious, and
removing the 'last' language makes it a tiny bit clearer that this bitmap
is special because we copied its contents into the TSS.

This makes code like this a tiny bit easier to read IMHO:

+ if (tss->io_bitmap.bitmap_copied_ptr != iobm ||
+ tss->io_bitmap.bitmap_copied_seq != iobm->sequence)

I marked it RFC because you might not agree. :-)

Only build tested.

Thanks,

Ingo

---
arch/x86/include/asm/processor.h | 10 +++++-----
arch/x86/kernel/cpu/common.c | 2 +-
arch/x86/kernel/process.c | 8 ++++----
3 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index d1f2c1eb14e9..b45ff7c1419f 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -367,12 +367,12 @@ struct entry_stack_page {
struct x86_io_bitmap
{
/*
- * The bitmap pointer and the sequence number of the last active
- * bitmap. last_bitmap cannot be dereferenced. It's solely for
- * comparison.
+ * The bitmap pointer and the sequence number of the last copied
+ * bitmap. bitmap_copied_ptr must not be dereferenced, it's solely
+ * for comparison.
*/
- struct io_bitmap *last_bitmap;
- u64 last_sequence;
+ const struct io_bitmap *bitmap_copied_ptr;
+ u64 bitmap_copied_seq;

/*
* Store the dirty size of the last io bitmap offender. The next
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index a35a557429e7..5a74c5b11b1c 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1861,7 +1861,7 @@ void cpu_init(void)
/* Initialize the TSS. */
tss_setup_ist(tss);
tss->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET_INVALID;
- tss->io_bitmap.last_bitmap = NULL;
+ tss->io_bitmap.bitmap_copied_ptr = NULL;
tss->io_bitmap.bytes_max = 0;
memset(tss->io_bitmap.map_bytes, 0xff, sizeof(tss->io_bitmap.map_bytes));
set_tss_desc(cpu, &get_cpu_entry_area(cpu)->tss.x86_tss);
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index c4e76a540b51..ecf97855ed68 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -358,8 +358,8 @@ static void tss_copy_io_bitmap(struct tss_struct *tss, struct io_bitmap *iobm)
* and a pointer to the bitmap itself.
*/
tss->io_bitmap.bytes_max = iobm->bytes_max;
- tss->io_bitmap.last_sequence = iobm->sequence;
- tss->io_bitmap.last_bitmap = iobm;
+ tss->io_bitmap.bitmap_copied_seq = iobm->sequence;
+ tss->io_bitmap.bitmap_copied_ptr = iobm;
}

/**
@@ -388,8 +388,8 @@ void tss_update_io_bitmap(void)
* sequence number differs. The update time is
* accounted to the incoming task.
*/
- if (tss->io_bitmap.last_bitmap != iobm ||
- tss->io_bitmap.last_sequence != iobm->sequence)
+ if (tss->io_bitmap.bitmap_copied_ptr != iobm ||
+ tss->io_bitmap.bitmap_copied_seq != iobm->sequence)
tss_copy_io_bitmap(tss, iobm);

/* Enable the bitmap */
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