diff options
author | Kevin Tian <kevin.tian@intel.com> | 2022-01-05 04:35:32 -0800 |
---|---|---|
committer | Paolo Bonzini <pbonzini@redhat.com> | 2022-01-14 13:44:43 -0500 |
commit | b5274b1b7ba89fe8ed38cc470041cd6ba0dfb79b (patch) | |
tree | 1f33da0fa4ac89d1b31c61655c37ad418e11aebc /arch/x86/include | |
parent | 5429cead01192ff4019ea0b13316268d14fd1ec2 (diff) | |
download | linux-b5274b1b7ba89fe8ed38cc470041cd6ba0dfb79b.tar.gz linux-b5274b1b7ba89fe8ed38cc470041cd6ba0dfb79b.tar.bz2 linux-b5274b1b7ba89fe8ed38cc470041cd6ba0dfb79b.zip |
kvm: x86: Disable interception for IA32_XFD on demand
Always intercepting IA32_XFD causes non-negligible overhead when this
register is updated frequently in the guest.
Disable r/w emulation after intercepting the first WRMSR(IA32_XFD)
with a non-zero value.
Disable WRMSR emulation implies that IA32_XFD becomes out-of-sync
with the software states in fpstate and the per-cpu xfd cache. This
leads to two additional changes accordingly:
- Call fpu_sync_guest_vmexit_xfd_state() after vm-exit to bring
software states back in-sync with the MSR, before handle_exit_irqoff()
is called.
- Always trap #NM once write interception is disabled for IA32_XFD.
The #NM exception is rare if the guest doesn't use dynamic
features. Otherwise, there is at most one exception per guest
task given a dynamic feature.
p.s. We have confirmed that SDM is being revised to say that
when setting IA32_XFD[18] the AMX register state is not guaranteed
to be preserved. This clarification avoids adding mess for a creative
guest which sets IA32_XFD[18]=1 before saving active AMX state to
its own storage.
Signed-off-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
Message-Id: <20220105123532.12586-22-yang.zhong@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/include')
-rw-r--r-- | arch/x86/include/asm/kvm_host.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 6cbf97a2ebc4..89d1fdb39c46 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -647,6 +647,7 @@ struct kvm_vcpu_arch { u64 smi_count; bool tpr_access_reporting; bool xsaves_enabled; + bool xfd_no_write_intercept; u64 ia32_xss; u64 microcode_version; u64 arch_capabilities; |