KVM: PPC: Book3S HV: Provide mode where all vCPUs on a core must be the same VM

BugLink: https://bugs.launchpad.net/bugs/1792957
This adds a mode where the vcore scheduling logic in HV KVM limits itself
to scheduling only virtual cores from the same VM on any given physical
core.  This is enabled via a new module parameter on the kvm-hv module
called "one_vm_per_core".  For this to work on POWER9, it is necessary to
set indep_threads_mode=N.  (On POWER8, hardware limitations mean that KVM
is never in independent threads mode, regardless of the indep_threads_mode
setting.)

Thus the settings needed for this to work are:

1. The host is in SMT1 mode.
2. On POWER8, the host is not in 2-way or 4-way static split-core mode.
3. On POWER9, the indep_threads_mode parameter is N.
4. The one_vm_per_core parameter is Y.

With these settings, KVM can run up to 4 vcpus on a core at the same
time on POWER9, or up to 8 vcpus on POWER8 (depending on the guest
threading mode), and will ensure that all of the vcpus belong to the
same VM.

This is intended for use in security-conscious settings where users are
concerned about possible side-channel attacks between threads which could
perhaps enable one VM to attack another VM on the same core, or the host.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
(cherry picked from commit aa2278644ae54ff762ce33f9c9563d759e9cca9f linux-next)
Signed-off-by: Joseph Salisbury <joseph.salisbury@canonical.com>
Acked-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index dc9eb6b495ce6c57549c121c9ddfa92f2c76d877..0c8a655c2e5decf9afc311bdacd7a702417b26ac 100644 (file)
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -103,6 +103,10 @@ static bool indep_threads_mode = true;
 module_param(indep_threads_mode, bool, S_IRUGO | S_IWUSR);
 MODULE_PARM_DESC(indep_threads_mode, "Independent-threads mode (only on POWER9)");
 
+static bool one_vm_per_core;
+module_param(one_vm_per_core, bool, S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(one_vm_per_core, "Only run vCPUs from the same VM on a core (requires indep_threads_mode=N)");
+
 #ifdef CONFIG_KVM_XICS
 static struct kernel_param_ops module_param_ops = {
        .set = param_set_int,
@@ -2449,6 +2453,10 @@ static bool can_dynamic_split(struct kvmppc_vcore *vc, struct core_info *cip)
        if (!cpu_has_feature(CPU_FTR_ARCH_207S))
                return false;
 
+       /* In one_vm_per_core mode, require all vcores to be from the same vm */
+       if (one_vm_per_core && vc->kvm != cip->vc[0]->kvm)
+               return false;
+
        /* Some POWER9 chips require all threads to be in the same MMU mode */
        if (no_mixing_hpt_and_radix &&
            kvm_is_radix(vc->kvm) != kvm_is_radix(cip->vc[0]->kvm))