1/* 2 * Asm versions of Xen pv-ops, suitable for either direct use or 3 * inlining. The inline versions are the same as the direct-use 4 * versions, with the pre- and post-amble chopped off. 5 * 6 * This code is encoded for size rather than absolute efficiency, with 7 * a view to being able to inline as much as possible. 8 * 9 * We only bother with direct forms (ie, vcpu in pda) of the 10 * operations here; the indirect forms are better handled in C, since 11 * they're generally too large to inline anyway. 12 */ 13 14#include <asm/thread_info.h> 15#include <asm/processor-flags.h> 16#include <asm/segment.h> 17 18#include <xen/interface/xen.h> 19 20#include "xen-asm.h" 21 22/* 23 * Force an event check by making a hypercall, but preserve regs 24 * before making the call. 25 */ 26check_events: 27 push %eax 28 push %ecx 29 push %edx 30 call xen_force_evtchn_callback 31 pop %edx 32 pop %ecx 33 pop %eax 34 ret 35 36/* 37 * We can't use sysexit directly, because we're not running in ring0. 38 * But we can easily fake it up using iret. Assuming xen_sysexit is 39 * jumped to with a standard stack frame, we can just strip it back to 40 * a standard iret frame and use iret. 41 */ 42ENTRY(xen_sysexit) 43 movl PT_EAX(%esp), %eax /* Shouldn't be necessary? */ 44 orl $X86_EFLAGS_IF, PT_EFLAGS(%esp) 45 lea PT_EIP(%esp), %esp 46 47 jmp xen_iret 48ENDPROC(xen_sysexit) 49 50/* 51 * This is run where a normal iret would be run, with the same stack setup: 52 * 8: eflags 53 * 4: cs 54 * esp-> 0: eip 55 * 56 * This attempts to make sure that any pending events are dealt with 57 * on return to usermode, but there is a small window in which an 58 * event can happen just before entering usermode. If the nested 59 * interrupt ends up setting one of the TIF_WORK_MASK pending work 60 * flags, they will not be tested again before returning to 61 * usermode. This means that a process can end up with pending work, 62 * which will be unprocessed until the process enters and leaves the 63 * kernel again, which could be an unbounded amount of time. This 64 * means that a pending signal or reschedule event could be 65 * indefinitely delayed. 66 * 67 * The fix is to notice a nested interrupt in the critical window, and 68 * if one occurs, then fold the nested interrupt into the current 69 * interrupt stack frame, and re-process it iteratively rather than 70 * recursively. This means that it will exit via the normal path, and 71 * all pending work will be dealt with appropriately. 72 * 73 * Because the nested interrupt handler needs to deal with the current 74 * stack state in whatever form its in, we keep things simple by only 75 * using a single register which is pushed/popped on the stack. 76 */ 77ENTRY(xen_iret) 78 /* test eflags for special cases */ 79 testl $(X86_EFLAGS_VM | XEN_EFLAGS_NMI), 8(%esp) 80 jnz hyper_iret 81 82 push %eax 83 ESP_OFFSET=4 # bytes pushed onto stack 84 85 /* 86 * Store vcpu_info pointer for easy access. Do it this way to 87 * avoid having to reload %fs 88 */ 89#ifdef CONFIG_SMP 90 GET_THREAD_INFO(%eax) 91 movl TI_cpu(%eax), %eax 92 movl __per_cpu_offset(,%eax,4), %eax 93 mov per_cpu__xen_vcpu(%eax), %eax 94#else 95 movl per_cpu__xen_vcpu, %eax 96#endif 97 98 /* check IF state we're restoring */ 99 testb $X86_EFLAGS_IF>>8, 8+1+ESP_OFFSET(%esp) 100 101 /* 102 * Maybe enable events. Once this happens we could get a 103 * recursive event, so the critical region starts immediately 104 * afterwards. However, if that happens we don't end up 105 * resuming the code, so we don't have to be worried about 106 * being preempted to another CPU. 107 */ 108 setz XEN_vcpu_info_mask(%eax) 109xen_iret_start_crit: 110 111 /* check for unmasked and pending */ 112 cmpw $0x0001, XEN_vcpu_info_pending(%eax) 113 114 /* 115 * If there's something pending, mask events again so we can 116 * jump back into xen_hypervisor_callback 117 */ 118 sete XEN_vcpu_info_mask(%eax) 119 120 popl %eax 121 122 /* 123 * From this point on the registers are restored and the stack 124 * updated, so we don't need to worry about it if we're 125 * preempted 126 */ 127iret_restore_end: 128 129 /* 130 * Jump to hypervisor_callback after fixing up the stack. 131 * Events are masked, so jumping out of the critical region is 132 * OK. 133 */ 134 je xen_hypervisor_callback 135 1361: iret 137xen_iret_end_crit: 138.section __ex_table, "a" 139 .align 4 140 .long 1b, iret_exc 141.previous 142 143hyper_iret: 144 /* put this out of line since its very rarely used */ 145 jmp hypercall_page + __HYPERVISOR_iret * 32 146 147 .globl xen_iret_start_crit, xen_iret_end_crit 148 149/* 150 * This is called by xen_hypervisor_callback in entry.S when it sees 151 * that the EIP at the time of interrupt was between 152 * xen_iret_start_crit and xen_iret_end_crit. We're passed the EIP in 153 * %eax so we can do a more refined determination of what to do. 154 * 155 * The stack format at this point is: 156 * ---------------- 157 * ss : (ss/esp may be present if we came from usermode) 158 * esp : 159 * eflags } outer exception info 160 * cs } 161 * eip } 162 * ---------------- <- edi (copy dest) 163 * eax : outer eax if it hasn't been restored 164 * ---------------- 165 * eflags } nested exception info 166 * cs } (no ss/esp because we're nested 167 * eip } from the same ring) 168 * orig_eax }<- esi (copy src) 169 * - - - - - - - - 170 * fs } 171 * es } 172 * ds } SAVE_ALL state 173 * eax } 174 * : : 175 * ebx }<- esp 176 * ---------------- 177 * 178 * In order to deliver the nested exception properly, we need to shift 179 * everything from the return addr up to the error code so it sits 180 * just under the outer exception info. This means that when we 181 * handle the exception, we do it in the context of the outer 182 * exception rather than starting a new one. 183 * 184 * The only caveat is that if the outer eax hasn't been restored yet 185 * (ie, it's still on stack), we need to insert its value into the 186 * SAVE_ALL state before going on, since it's usermode state which we 187 * eventually need to restore. 188 */ 189ENTRY(xen_iret_crit_fixup) 190 /* 191 * Paranoia: Make sure we're really coming from kernel space. 192 * One could imagine a case where userspace jumps into the 193 * critical range address, but just before the CPU delivers a 194 * GP, it decides to deliver an interrupt instead. Unlikely? 195 * Definitely. Easy to avoid? Yes. The Intel documents 196 * explicitly say that the reported EIP for a bad jump is the 197 * jump instruction itself, not the destination, but some 198 * virtual environments get this wrong. 199 */ 200 movl PT_CS(%esp), %ecx 201 andl $SEGMENT_RPL_MASK, %ecx 202 cmpl $USER_RPL, %ecx 203 je 2f 204 205 lea PT_ORIG_EAX(%esp), %esi 206 lea PT_EFLAGS(%esp), %edi 207 208 /* 209 * If eip is before iret_restore_end then stack 210 * hasn't been restored yet. 211 */ 212 cmp $iret_restore_end, %eax 213 jae 1f 214 215 movl 0+4(%edi), %eax /* copy EAX (just above top of frame) */ 216 movl %eax, PT_EAX(%esp) 217 218 lea ESP_OFFSET(%edi), %edi /* move dest up over saved regs */ 219 220 /* set up the copy */ 2211: std 222 mov $PT_EIP / 4, %ecx /* saved regs up to orig_eax */ 223 rep movsl 224 cld 225 226 lea 4(%edi), %esp /* point esp to new frame */ 2272: jmp xen_do_upcall 228 229