Keir Fraser wrote:
My only argument in favor of using the lock would be for completeness
of the emulation. You are
absolutely right in that for Linux there seems to be no need to hold
the lock. My concern is that
other OSs may treat this differently. And if we don't have sources,
it may be somewhat difficult
to figure out that the atomicity (or lack of it) was the cause of a
problem.
If, however, there is a strong feeling that we don't need the lock, I
am happy to drop it.
I guess you are mostly unhappy about adding a new field to
hvm_domain, not about performance
impact?
Yes, also my second argument was that there is *no way* for two VCPUs
to conflict on a local APIC access, since LAPIC accesses are always to
the VCPU's own LAPIC. So there is no potential concurrency that needs
to be serialised, regardless of the guest OS.
OK, that's fair. Here is updated patch with lock removed.
I don't think I then understand why Linux is using atomic accesses to
local APICs. It's interesting though that 64-bit code doesn't do it ---
they use vanilla apic_write().
-boris
#
# Add support for XCHG instruction accessing APIC
#
Signed-off-by: Boris Ostrovsky <bostrovsky@xxxxxxxxxxxxxxx>
diff -r d0d3fef37685 xen/Rules.mk
--- a/xen/Rules.mk Mon Apr 3 14:34:20 2006 +0100
+++ b/xen/Rules.mk Wed Apr 5 10:18:35 2006 -0400
@@ -31,6 +31,9 @@ HDRS += $(wildcard $(BASEDIR)/include
HDRS += $(wildcard $(BASEDIR)/include/public/*.h)
HDRS += $(wildcard $(BASEDIR)/include/asm-$(TARGET_ARCH)/*.h)
HDRS += $(wildcard
$(BASEDIR)/include/asm-$(TARGET_ARCH)/$(TARGET_SUBARCH)/*.h)
+HDRS += $(wildcard $(BASEDIR)/include/asm-$(TARGET_ARCH)/hvm/*.h)
+HDRS += $(wildcard $(BASEDIR)/include/asm-$(TARGET_ARCH)/hvm/svm/*.h)
+HDRS += $(wildcard $(BASEDIR)/include/asm-$(TARGET_ARCH)/hvm/vmx/*.h)
# Do not depend on auto-generated header files.
HDRS := $(subst
$(BASEDIR)/include/asm-$(TARGET_ARCH)/asm-offsets.h,,$(HDRS))
HDRS := $(subst $(BASEDIR)/include/xen/banner.h,,$(HDRS))
diff -r d0d3fef37685 xen/arch/x86/hvm/intercept.c
--- a/xen/arch/x86/hvm/intercept.c Mon Apr 3 14:34:20 2006 +0100
+++ b/xen/arch/x86/hvm/intercept.c Wed Apr 5 10:18:35 2006 -0400
@@ -123,6 +123,16 @@ static inline void hvm_mmio_access(struc
req->u.data = tmp1;
break;
+ case IOREQ_TYPE_XCHG:
+ /*
+ * Note that we don't need to be atomic here since VCPU is accessing
+ * its own local APIC.
+ */
+ tmp1 = read_handler(v, req->addr, req->size);
+ write_handler(v, req->addr, req->size, (unsigned long) req->u.data);
+ req->u.data = tmp1;
+ break;
+
default:
printk("error ioreq type for local APIC %x\n", req->type);
domain_crash_synchronous();
@@ -143,7 +153,7 @@ int hvm_mmio_intercept(ioreq_t *p)
if ( hvm_mmio_handlers[i]->check_handler(v, p->addr) ) {
hvm_mmio_access(v, p,
hvm_mmio_handlers[i]->read_handler,
- hvm_mmio_handlers[i]->write_handler);
+ hvm_mmio_handlers[i]->write_handler);
return 1;
}
}
diff -r d0d3fef37685 xen/arch/x86/hvm/platform.c
--- a/xen/arch/x86/hvm/platform.c Mon Apr 3 14:34:20 2006 +0100
+++ b/xen/arch/x86/hvm/platform.c Wed Apr 5 10:18:35 2006 -0400
@@ -439,6 +439,14 @@ static int hvm_decode(int realmode, unsi
GET_OP_SIZE_FOR_BYTE(size_reg);
return mem_reg(size_reg, opcode, instr, rex);
+ case 0x87: /* xchg {r/m16|r/m32}, {m/r16|m/r32} */
+ instr->instr = INSTR_XCHG;
+ GET_OP_SIZE_FOR_NONEBYTE(instr->op_size);
+ if (((*(opcode+1)) & 0xc7) == 5)
+ return reg_mem(instr->op_size, opcode, instr, rex);
+ else
+ return mem_reg(instr->op_size, opcode, instr, rex);
+
case 0x88: /* mov r8, m8 */
instr->instr = INSTR_MOV;
instr->op_size = BYTE;
@@ -936,6 +944,17 @@ void handle_mmio(unsigned long va, unsig
break;
}
+ case INSTR_XCHG:
+ mmio_opp->flags = mmio_inst.flags;
+ mmio_opp->instr = mmio_inst.instr;
+ mmio_opp->operand[0] = mmio_inst.operand[0]; /* source */
+ mmio_opp->operand[1] = mmio_inst.operand[1]; /* destination */
+
+ /* send the request and wait for the value */
+ send_mmio_req(IOREQ_TYPE_XCHG, gpa, 1,
+ mmio_inst.op_size, 0, IOREQ_WRITE, 0);
+ break;
+
default:
printf("Unhandled MMIO instruction\n");
domain_crash_synchronous();
diff -r d0d3fef37685 xen/include/asm-x86/hvm/io.h
--- a/xen/include/asm-x86/hvm/io.h Mon Apr 3 14:34:20 2006 +0100
+++ b/xen/include/asm-x86/hvm/io.h Wed Apr 5 10:18:35 2006 -0400
@@ -66,6 +66,7 @@
#define INSTR_STOS 10
#define INSTR_TEST 11
#define INSTR_BT 12
+#define INSTR_XCHG 13
struct instruction {
__s8 instr; /* instruction type */
diff -r d0d3fef37685 xen/include/public/hvm/ioreq.h
--- a/xen/include/public/hvm/ioreq.h Mon Apr 3 14:34:20 2006 +0100
+++ b/xen/include/public/hvm/ioreq.h Wed Apr 5 10:18:35 2006 -0400
@@ -34,6 +34,7 @@
#define IOREQ_TYPE_AND 2
#define IOREQ_TYPE_OR 3
#define IOREQ_TYPE_XOR 4
+#define IOREQ_TYPE_XCHG 5
/*
* VMExit dispatcher should cooperate with instruction decoder to
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