From: Suraj Jitindar Singh sjitindarsingh@gmail.com
commit c8b4083db915dfe5a3b4a755ad2317e0509b43f1 upstream.
The Performance Stop Status and Control Register (PSSCR) is used to control the power saving facilities of the processor. This register has various fields, some of which can be modified only in hypervisor state, and others which can be modified in both hypervisor and privileged non-hypervisor state. The bits which can be modified in privileged non-hypervisor state are referred to as guest visible.
Currently the L0 hypervisor saves and restores both it's own host value as well as the guest value of the PSSCR when context switching between the hypervisor and guest. However a nested hypervisor running it's own nested guests (as indicated by kvmhv_on_pseries()) doesn't context switch the PSSCR register. That means if a nested (L2) guest modifies the PSSCR then the L1 guest hypervisor will run with that modified value, and if the L1 guest hypervisor modifies the PSSCR and then goes to run the nested (L2) guest again then the L2 PSSCR value will be lost.
Fix this by having the (L1) nested hypervisor save and restore both its host and the guest PSSCR value when entering and exiting a nested (L2) guest. Note that only the guest visible parts of the PSSCR are context switched since this is all the L1 nested hypervisor can access, this is fine however as these are the only fields the L0 hypervisor provides guest control of anyway and so all other fields are ignored.
This could also have been implemented by adding the PSSCR register to the hv_regs passed to the L0 hypervisor as input to the H_ENTER_NESTED hcall, however this would have meant updating the structure layout and thus required modifications to both the L0 and L1 kernels. Whereas the approach used doesn't require L0 kernel modifications while achieving the same result.
Fixes: 95a6432ce903 ("KVM: PPC: Book3S HV: Streamlined guest entry/exit path on P9 for radix guests") Cc: stable@vger.kernel.org # v4.20+ Signed-off-by: Suraj Jitindar Singh sjitindarsingh@gmail.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20190703012022.15644-3-sjitindarsingh@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/powerpc/kvm/book3s_hv.c | 11 +++++++++++ 1 file changed, 11 insertions(+)
--- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -3569,9 +3569,18 @@ int kvmhv_p9_guest_entry(struct kvm_vcpu mtspr(SPRN_DEC, vcpu->arch.dec_expires - mftb());
if (kvmhv_on_pseries()) { + /* + * We need to save and restore the guest visible part of the + * psscr (i.e. using SPRN_PSSCR_PR) since the hypervisor + * doesn't do this for us. Note only required if pseries since + * this is done in kvmhv_load_hv_regs_and_go() below otherwise. + */ + unsigned long host_psscr; /* call our hypervisor to load up HV regs and go */ struct hv_guest_state hvregs;
+ host_psscr = mfspr(SPRN_PSSCR_PR); + mtspr(SPRN_PSSCR_PR, vcpu->arch.psscr); kvmhv_save_hv_regs(vcpu, &hvregs); hvregs.lpcr = lpcr; vcpu->arch.regs.msr = vcpu->arch.shregs.msr; @@ -3590,6 +3599,8 @@ int kvmhv_p9_guest_entry(struct kvm_vcpu vcpu->arch.shregs.msr = vcpu->arch.regs.msr; vcpu->arch.shregs.dar = mfspr(SPRN_DAR); vcpu->arch.shregs.dsisr = mfspr(SPRN_DSISR); + vcpu->arch.psscr = mfspr(SPRN_PSSCR_PR); + mtspr(SPRN_PSSCR_PR, host_psscr);
/* H_CEDE has to be handled now, not later */ if (trap == BOOK3S_INTERRUPT_SYSCALL && !vcpu->arch.nested &&