From ec35d23a92530b527e30788d85d99a161f226974 Mon Sep 17 00:00:00 2001 From: Keir Fraser Date: Mon, 14 Dec 2009 07:59:40 +0000 Subject: [PATCH] docs: add a document about guest cpuid configuration Signed-off-by: Dexuan Cui --- docs/misc/cpuid-config-for-guest.txt | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) create mode 100644 docs/misc/cpuid-config-for-guest.txt diff --git a/docs/misc/cpuid-config-for-guest.txt b/docs/misc/cpuid-config-for-guest.txt new file mode 100644 index 0000000000..1614dfed7e --- /dev/null +++ b/docs/misc/cpuid-config-for-guest.txt @@ -0,0 +1,23 @@ +CPUID emulation for guest +------------------------- + +When HVM guest tries to execute CPUID, or PV guest tries to execute XEN_CPUID, +the xen hypervior traps and emultes them. + +For HVM guest and PV DomU guest, xen's CPUID emulation can be adjusted using +the guest configation file if necessary (e.g., to supply better support for +guest live migration). The CPUID syntax in guest configration file is +described in detail in the examples like /etc/xen/xmexample.hvm, +/etc/xen/xmexample.hvm-stubdom. + +However, a user (or an administrator) must be aware that the CPUID in guest +configuration file can NOT be configured casually. The default CPUID +configuration should be safe, but illegal configuration can cause unexpected +behaviors of guest -- even can crash guest. + +For example, we should not expose the MONITOR CPUID feature flag (ECX bit 3; +CPUID executed EAX = 1) to HVM guest, otherwise, on guest's attempt of +executing MWAIT, the VMExit handler in Xen would inject #UD (Invalid Opcode +Exception) into the HVM guest, and guest kernel would panic. + +/* We can add more unsafe CPUID configuration here in future. */ -- 2.30.2