The following commit has been merged in the linux branch: commit 2c75910f1aa042be1dd769378d2611bf551721ac Author: Chris Lalancette clalance@redhat.com Date: Thu Nov 5 11:47:08 2009 +0100
x86: Make sure get_user_desc() doesn't sign extend.
The current implementation of get_user_desc() sign extends the return value because of integer promotion rules. For the most part, this doesn't matter, because the top bit of base2 is usually 0. If, however, that bit is 1, then the entire value will be 0xffff... which is probably not what the caller intended.
This patch casts the entire thing to unsigned before returning, which generates almost the same assembly as the current code but replaces the final "cltq" (sign extend) with a "mov %eax %eax" (zero-extend). This fixes booting certain guests under KVM.
Signed-off-by: Chris Lalancette clalance@redhat.com Signed-off-by: Linus Torvalds torvalds@linux-foundation.org
diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h index e8de2f6..617bd56 100644 --- a/arch/x86/include/asm/desc.h +++ b/arch/x86/include/asm/desc.h @@ -288,7 +288,7 @@ static inline void load_LDT(mm_context_t *pc)
static inline unsigned long get_desc_base(const struct desc_struct *desc) { - return desc->base0 | ((desc->base1) << 16) | ((desc->base2) << 24); + return (unsigned)(desc->base0 | ((desc->base1) << 16) | ((desc->base2) << 24)); }
static inline void set_desc_base(struct desc_struct *desc, unsigned long base)