diff options
Diffstat (limited to 'arch/x86/xen/xen-asm_32.S')
| -rw-r--r-- | arch/x86/xen/xen-asm_32.S | 73 |
1 files changed, 24 insertions, 49 deletions
diff --git a/arch/x86/xen/xen-asm_32.S b/arch/x86/xen/xen-asm_32.S index 8b8f8355b938..2712e9155306 100644 --- a/arch/x86/xen/xen-asm_32.S +++ b/arch/x86/xen/xen-asm_32.S @@ -127,10 +127,9 @@ SYM_CODE_END(xen_iret) .globl xen_iret_start_crit, xen_iret_end_crit /* - * This is called by xen_hypervisor_callback in entry.S when it sees + * This is called by xen_hypervisor_callback in entry_32.S when it sees * that the EIP at the time of interrupt was between - * xen_iret_start_crit and xen_iret_end_crit. We're passed the EIP in - * %eax so we can do a more refined determination of what to do. + * xen_iret_start_crit and xen_iret_end_crit. * * The stack format at this point is: * ---------------- @@ -139,70 +138,46 @@ SYM_CODE_END(xen_iret) * eflags } outer exception info * cs } * eip } - * ---------------- <- edi (copy dest) - * eax : outer eax if it hasn't been restored * ---------------- - * eflags } nested exception info - * cs } (no ss/esp because we're nested - * eip } from the same ring) - * orig_eax }<- esi (copy src) - * - - - - - - - - - * fs } - * es } - * ds } SAVE_ALL state - * eax } - * : : - * ebx }<- esp + * eax : outer eax if it hasn't been restored * ---------------- + * eflags } + * cs } nested exception info + * eip } + * return address : (into xen_hypervisor_callback) * - * In order to deliver the nested exception properly, we need to shift - * everything from the return addr up to the error code so it sits - * just under the outer exception info. This means that when we - * handle the exception, we do it in the context of the outer - * exception rather than starting a new one. + * In order to deliver the nested exception properly, we need to discard the + * nested exception frame such that when we handle the exception, we do it + * in the context of the outer exception rather than starting a new one. * - * The only caveat is that if the outer eax hasn't been restored yet - * (ie, it's still on stack), we need to insert its value into the - * SAVE_ALL state before going on, since it's usermode state which we - * eventually need to restore. + * The only caveat is that if the outer eax hasn't been restored yet (i.e. + * it's still on stack), we need to restore its value here. */ SYM_CODE_START(xen_iret_crit_fixup) /* * Paranoia: Make sure we're really coming from kernel space. * One could imagine a case where userspace jumps into the * critical range address, but just before the CPU delivers a - * GP, it decides to deliver an interrupt instead. Unlikely? - * Definitely. Easy to avoid? Yes. The Intel documents - * explicitly say that the reported EIP for a bad jump is the - * jump instruction itself, not the destination, but some - * virtual environments get this wrong. + * PF, it decides to deliver an interrupt instead. Unlikely? + * Definitely. Easy to avoid? Yes. */ - movl PT_CS(%esp), %ecx - andl $SEGMENT_RPL_MASK, %ecx - cmpl $USER_RPL, %ecx - je 2f - - lea PT_ORIG_EAX(%esp), %esi - lea PT_EFLAGS(%esp), %edi + testb $2, 2*4(%esp) /* nested CS */ + jnz 2f /* * If eip is before iret_restore_end then stack * hasn't been restored yet. */ - cmp $iret_restore_end, %eax + cmpl $iret_restore_end, 1*4(%esp) jae 1f - movl 0+4(%edi), %eax /* copy EAX (just above top of frame) */ - movl %eax, PT_EAX(%esp) - - lea ESP_OFFSET(%edi), %edi /* move dest up over saved regs */ + movl 4*4(%esp), %eax /* load outer EAX */ + ret $4*4 /* discard nested EIP, CS, and EFLAGS as + * well as the just restored EAX */ - /* set up the copy */ -1: std - mov $PT_EIP / 4, %ecx /* saved regs up to orig_eax */ - rep movsl - cld +1: + ret $3*4 /* discard nested EIP, CS, and EFLAGS */ - lea 4(%edi), %esp /* point esp to new frame */ -2: jmp xen_do_upcall +2: + ret SYM_CODE_END(xen_iret_crit_fixup) |