lkml.org 
[lkml]   [2022]   [Jan]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [DROP][PATCH] KVM: x86: Fix the #GP(0) and #UD conditions for XSETBV emulation
From
On 1/20/22 08:48, Like Xu wrote:
>
> In the testcase "executing XSETBV with CR4.XSAVE=0",
>
> - on the VMX, #UD delivery does not require vm-exit;

Not your fault, it would be nicer if the Intel manual told the truth;
it says: "The following instructions cause VM exits when they are
executed in VMX non-root operation: CPUID, GETSEC[1], INVD, and XSETBV."

Footnote [1] says "An execution of GETSEC causes an invalid-opcode
exception (#UD) if CR4.SMXE[Bit 14] = 0", and there is no such footnote
for XSETBV. Nevertheless, when tracing xsave.flat, I see that there's
a #UD vmexit and not an XSETBV vmexit:

qemu-kvm-1637698 [019] 758186.750321: kvm_entry: vcpu 0, rip 0x4028b7
qemu-kvm-1637698 [019] 758186.750322: kvm_exit: vcpu 0 reason EXCEPTION_NMI rip 0x40048d info1 0x0000000000000000 info2 0x0000000000000000 intr_info 0x80000306 error_code 0x00000000
qemu-kvm-1637698 [019] 758186.750324: kvm_emulate_insn: 0:40048d:0f 01 d1 (prot64)
qemu-kvm-1637698 [019] 758186.750325: kvm_inj_exception: #UD (0x0)

So while my gut feeling that #UD would not cause a vmexit was correct,
technically I was reading the SDM incorrectly.

Jun, can you have this fixed?

Paolo

> - on the SVM, #UD is trapped but goes to the ud_interception() path;

\
 
 \ /
  Last update: 2022-01-20 10:19    [W:0.055 / U:0.032 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site