On 2019-11-05 3:56 p.m., Paolo Bonzini wrote:
On 05/11/19 17:17, Vitaly Kuznetsov wrote:
There is also one additional piece of the information missing. A VM can be
sharing physical cores with other VMs (or other userspace tasks on the
host) so does KVM_FEATURE_TRUSTWORTHY_SMT imply that it's not the case or
not? It is unclear if this changes anything and can probably be left out
of scope (just don't do that).
Similar to the already existent 'NoNonArchitecturalCoreSharing' Hyper-V
enlightenment, the default value of KVM_HINTS_TRUSTWORTHY_SMT is set to
!cpu_smt_possible(). KVM userspace is thus supposed to pass it to guest's
CPUIDs in case it is '1' (meaning no SMT on the host at all) or do some
extra work (like CPU pinning and exposing the correct topology) before
passing '1' to the guest.
Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
Documentation/virt/kvm/cpuid.rst | 27 +++++++++++++++++++--------
arch/x86/include/uapi/asm/kvm_para.h | 2 ++
arch/x86/kvm/cpuid.c | 7 ++++++-
3 files changed, 27 insertions(+), 9 deletions(-)
diff --git a/Documentation/virt/kvm/cpuid.rst b/Documentation/virt/kvm/cpuid.rst
index 01b081f6e7ea..64b94103fc90 100644
--- a/Documentation/virt/kvm/cpuid.rst
+++ b/Documentation/virt/kvm/cpuid.rst
@@ -86,6 +86,10 @@ KVM_FEATURE_PV_SCHED_YIELD 13 guest checks this feature bit
before using paravirtualized
sched yield.
+KVM_FEATURE_TRUSTWORTHY_SMT 14 set when host supports 'SMT
+ topology is trustworthy' hint
+ (KVM_HINTS_TRUSTWORTHY_SMT).
+
Instead of defining a one-off bit, can we make:
ecx = the set of known "hints" (defaults to edx if zero)
edx = the set of hints that apply to the virtual machine
Just to resurrect this thread, the guest could explicitly ACK
a KVM_FEATURE_DYNAMIC_HINT at init. This would allow the host
to change the hints whenever with the guest not needing to separately
ACK the changed hints.
Ankur
Paolo
6
