diff options
Diffstat (limited to 'arch/x86/lguest/head_32.S')
| -rw-r--r-- | arch/x86/lguest/head_32.S | 30 |
1 files changed, 13 insertions, 17 deletions
diff --git a/arch/x86/lguest/head_32.S b/arch/x86/lguest/head_32.S index 6ddfe4f..d5ae63f 100644 --- a/arch/x86/lguest/head_32.S +++ b/arch/x86/lguest/head_32.S @@ -84,7 +84,7 @@ ENTRY(lg_irq_enable) * set lguest_data.irq_pending to X86_EFLAGS_IF. If it's not zero, we * jump to send_interrupts, otherwise we're done. */ - testl $0, lguest_data+LGUEST_DATA_irq_pending + cmpl $0, lguest_data+LGUEST_DATA_irq_pending jnz send_interrupts /* * One cool thing about x86 is that you can do many things without using @@ -133,9 +133,8 @@ ENTRY(lg_restore_fl) ret /*:*/ -/* These demark the EIP range where host should never deliver interrupts. */ -.global lguest_noirq_start -.global lguest_noirq_end +/* These demark the EIP where host should never deliver interrupts. */ +.global lguest_noirq_iret /*M:004 * When the Host reflects a trap or injects an interrupt into the Guest, it @@ -168,29 +167,26 @@ ENTRY(lg_restore_fl) * So we have to copy eflags from the stack to lguest_data.irq_enabled before * we do the "iret". * - * There are two problems with this: firstly, we need to use a register to do - * the copy and secondly, the whole thing needs to be atomic. The first - * problem is easy to solve: push %eax on the stack so we can use it, and then - * restore it at the end just before the real "iret". + * There are two problems with this: firstly, we can't clobber any registers + * and secondly, the whole thing needs to be atomic. The first problem + * is solved by using "push memory"/"pop memory" instruction pair for copying. * * The second is harder: copying eflags to lguest_data.irq_enabled will turn * interrupts on before we're finished, so we could be interrupted before we - * return to userspace or wherever. Our solution to this is to surround the - * code with lguest_noirq_start: and lguest_noirq_end: labels. We tell the + * return to userspace or wherever. Our solution to this is to tell the * Host that it is *never* to interrupt us there, even if interrupts seem to be - * enabled. + * enabled. (It's not necessary to protect pop instruction, since + * data gets updated only after it completes, so we only need to protect + * one instruction, iret). */ ENTRY(lguest_iret) - pushl %eax - movl 12(%esp), %eax -lguest_noirq_start: + pushl 2*4(%esp) /* * Note the %ss: segment prefix here. Normal data accesses use the * "ds" segment, but that will have already been restored for whatever * we're returning to (such as userspace): we can't trust it. The %ss: * prefix makes sure we use the stack segment, which is still valid. */ - movl %eax,%ss:lguest_data+LGUEST_DATA_irq_enabled - popl %eax + popl %ss:lguest_data+LGUEST_DATA_irq_enabled +lguest_noirq_iret: iret -lguest_noirq_end: |
