The question is about the VM-exit instruction length field. This is accessed in xen via:
__vmread(VM_EXIT_INSTRUCTION_LEN, &inst_len); an example of which is in routine get_instruction_length(). Is it architecturally defined that #GP intercept vmexits on IN and OUT actually set this field? What about other instructions? My reading of (directly out of "Intel® 64 and IA-32 Architectures Software Developer’s Manual Volume 3 (3A, 3B & 3C): System Programming Guide Order Number: 325384-052US, September 2014"): • VM-exit instruction length. This field is used in the following cases: — For fault-like VM exits due to attempts to execute one of the following instructions that cause VM exits unconditionally (see Section 25.1.2) or based on the settings of VM-execution controls (see Section 25.1.3): CLTS, CPUID, GETSEC, HLT, IN, INS, INVD, INVEPT, INVLPG, INVPCID, INVVPID, LGDT, LIDT, LLDT, LMSW, LTR, MONITOR, MOV CR, MOV DR, MWAIT, OUT, OUTS, PAUSE, RDMSR, RDPMC, RDRAND, RDSEED, RDTSC, RDTSCP, RSM, SGDT, SIDT, SLDT, STR, VMCALL, VMCLEAR, VMLAUNCH, VMPTRLD, VMPTRST, VMREAD, VMRESUME, VMWRITE, VMXOFF, VMXON, WBINVD, WRMSR, XRSTORS, XSETBV, and XSAVES. And 25.1.2 Instructions That Cause VM Exits Unconditionally The following instructions cause VM exits when they are executed in VMX non-root operation: CPUID, GETSEC,1 INVD, and XSETBV. This is also true of instructions introduced with VMX, which include: INVEPT, INVVPID, VMCALL,2 VMCLEAR, VMLAUNCH, VMPTRLD, VMPTRST, VMRESUME, VMXOFF, and VMXON. 25.1.3 Instructions That Cause VM Exits Conditionally Certain instructions cause VM exits in VMX non-root operation depending on the setting of the VM-execution controls. The following instructions can cause “fault-like” VM exits based on the conditions described:3 • CLTS. The CLTS instruction causes a VM exit if the bits in position 3 (corresponding to CR0.TS) are set in both the CR0 guest/host mask and the CR0 read shadow. • HLT. The HLT instruction causes a VM exit if the “HLT exiting” VM-execution control is 1. • IN, INS/INSB/INSW/INSD, OUT, OUTS/OUTSB/OUTSW/OUTSD. The behavior of each of these instruc- tions is determined by the settings of the “unconditional I/O exiting” and “use I/O bitmaps” VM-execution controls: — If both controls are 0, the instruction executes normally. — If the “unconditional I/O exiting” VM-execution control is 1 and the “use I/O bitmaps” VM-execution control is 0, the instruction causes a VM exit. — If the “use I/O bitmaps” VM-execution control is 1, the instruction causes a VM exit if it attempts to access an I/O port corresponding to a bit set to 1 in the appropriate I/O bitmap (see Section 24.6.4). If an I/O operation “wraps around” the 16-bit I/O-port space (accesses ports FFFFH and 0000H), the I/O instruction causes a VM exit (the “unconditional I/O exiting” VM-execution control is ignored if the “use I/O bitmaps” VM-execution control is 1). See Section 25.1.1 for information regarding the priority of VM exits relative to faults that may be caused by the INS and OUTS instructions. to me says that yes, this field is set on a #GP exit on an IN or an OUT. But the #GP case is not called out by name. To know if it is safe to use VM-exit instruction length in #GP fault handling code? -Don Slutz _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
