On Fri Sep 13, 2024 at 6:02 PM UTC, Sean Christopherson wrote:

On Sun, Jun 09, 2024, Nicolas Saenz Julienne wrote:

quoted

HvCallSendSyntheticClusterIpi and HvCallSendSyntheticClusterIpiEx allow
sending VTL-aware IPIs. Honour the hcall by exiting to user-space upon
receiving a request with a valid VTL target. This behaviour is only
available if the VSM CPUID flag is available and exposed to the guest.
It doesn't introduce a behaviour change otherwise.

User-space is accountable for the correct processing of the PV-IPI
before resuming execution.

Signed-off-by: Nicolas Saenz Julienne <redacted>
---
 arch/x86/kvm/hyperv.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 42f44546fe79c..d00baf3ffb165 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c

@@ -2217,16 +2217,20 @@ static void kvm_hv_send_ipi_to_many(struct kvm *kvm, u32 vector,

 static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
 {
+     bool vsm_enabled = kvm_hv_cpuid_vsm_enabled(vcpu);
      struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
      u64 *sparse_banks = hv_vcpu->sparse_banks;
      struct kvm *kvm = vcpu->kvm;
      struct hv_send_ipi_ex send_ipi_ex;
      struct hv_send_ipi send_ipi;
+     union hv_input_vtl *in_vtl;
      u64 valid_bank_mask;
+     int rsvd_shift;
      u32 vector;
      bool all_cpus;

      if (hc->code == HVCALL_SEND_IPI) {
+             in_vtl = &send_ipi.in_vtl;

I don't see any value in having a local pointer to a union.  Just use send_ipi.in_vtl.

OK, I'll simplify it.

quoted

              if (!hc->fast) {
                      if (unlikely(kvm_read_guest(kvm, hc->ingpa, &send_ipi,
                                                  sizeof(send_ipi))))

@@ -2235,16 +2239,22 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
                      vector = send_ipi.vector;
              } else {
                      /* 'reserved' part of hv_send_ipi should be 0 */
-                     if (unlikely(hc->ingpa >> 32 != 0))
+                     rsvd_shift = vsm_enabled ? 40 : 32;
+                     if (unlikely(hc->ingpa >> rsvd_shift != 0))
                              return HV_STATUS_INVALID_HYPERCALL_INPUT;

The existing error handling doesn't make any sense to me.  Why is this the _only_
path that enforces reserved bits?

I don't know.

As far as I can tell, the hypercall was introduced in v5 of the TLFS and
already contained the VTL selection bits. Unfortunately the spec doesn't
explicitly state what to do when hv_input_vtl is received from a non-VSM
enabled guest, so I tried to keep the current behaviour for every case
(send_ipi/send_ipi_ex/fast/!fat).

Regarding the shift, I think it makes more sense to do:

                        /* Bits 63:40 are always reserved. */
                        if (unlikely(hc->ingpa >> 40 != 0))
                                return HV_STATUS_INVALID_HYPERCALL_INPUT;

                        send_ipi.in_vtl.as_uint8 = (u8)(hc->ingpa >> 32);
                        if (unlikely(!vsm_enabled && send_ipi.in_vtl.as_uint8))
                                return HV_STATUS_INVALID_HYPERCALL_INPUT;

so that it's more obvious exactly what is/isn't reserved when VSM isn't/is enabled.

OK, I agree it's nicer.

quoted

+                     in_vtl->as_uint8 = (u8)(hc->ingpa >> 32);
                      sparse_banks[0] = hc->outgpa;
                      vector = (u32)hc->ingpa;
              }
              all_cpus = false;
              valid_bank_mask = BIT_ULL(0);

+             if (in_vtl->use_target_vtl)

Due to the lack of error checking for the !hc->fast case, this will do the wrong
thing if vsm_enabled=false.

Yes. I'll fix it.

Thanks,
Nicolas