Re: [PATCH v2 22/30] KVM: s390: intercept the rpcit instruction

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On 1/18/22 18:27, Matthew Rosato wrote:
On 1/18/22 6:05 AM, Pierre Morel wrote:


On 1/14/22 21:31, Matthew Rosato wrote:
For faster handling of PCI translation refreshes, intercept in KVM
and call the associated handler.

Signed-off-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxx>
---
  arch/s390/kvm/priv.c | 46 ++++++++++++++++++++++++++++++++++++++++++++
  1 file changed, 46 insertions(+)

diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
index 417154b314a6..5b65c1830de2 100644
--- a/arch/s390/kvm/priv.c
+++ b/arch/s390/kvm/priv.c
@@ -29,6 +29,7 @@
  #include <asm/ap.h>
  #include "gaccess.h"
  #include "kvm-s390.h"
+#include "pci.h"
  #include "trace.h"
  static int handle_ri(struct kvm_vcpu *vcpu)
@@ -335,6 +336,49 @@ static int handle_rrbe(struct kvm_vcpu *vcpu)
      return 0;
  }
+static int handle_rpcit(struct kvm_vcpu *vcpu)
+{
+    int reg1, reg2;
+    u8 status;
+    int rc;
+
+    if (vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE)
+        return kvm_s390_inject_program_int(vcpu, PGM_PRIVILEGED_OP);
+
+    /* If the host doesn't support PCI, it must be an emulated device */
+    if (!IS_ENABLED(CONFIG_PCI))
+        return -EOPNOTSUPP;

AFAIU this makes also sure that the following code is not compiled in case PCI is not supported.

I am not very used to compilation options, is it true with all our compilers and options?
Or do we have to specify a compiler version?

Another concern is, shouldn't we use IS_ENABLED(CONFIG_VFIO_PCI) ?

Same idea as in the other thread -- What we are trying to protect against here is referencing symbols that won't be linked (like zpci_refresh_trans, or the aift->mdd a few lines below)

It is indeed true that we should never need to handle the rpcit intercept in KVM if CONFIG_VFIO_PCI=n -- but the necessary symbols/code are linked at least, so we can just let the SHM logic sort this out. When CONFIG_PCI=y|m, arch/s390/kvm/pci.o will be linked and so we can compare the function handle against afit->mdd (check to see if the device is emulated) and use this to determine whether or not to immediately send to userspace -- And if CONFIG_VFIO_PCI=n, a SHM bit will always be on and so we'll always go to userspace via this check.

So we agree.
But as I I said somewhere else I wonder if CONFIG_VFIO_PCI_ZDEV would not even be better here.





+
+    kvm_s390_get_regs_rre(vcpu, &reg1, &reg2);
+
+    /* If the device has a SHM bit on, let userspace take care of this */
+    if (((vcpu->run->s.regs.gprs[reg1] >> 32) & aift->mdd) != 0)
+        return -EOPNOTSUPP;
+
+    rc = kvm_s390_pci_refresh_trans(vcpu, vcpu->run->s.regs.gprs[reg1],
+                    vcpu->run->s.regs.gprs[reg2],
+                    vcpu->run->s.regs.gprs[reg2+1],
+                    &status);
+
+    switch (rc) {
+    case 0:
+        kvm_s390_set_psw_cc(vcpu, 0);
+        break;
+    case -EOPNOTSUPP:
+        return -EOPNOTSUPP;
+    default:
+        vcpu->run->s.regs.gprs[reg1] &= 0xffffffff00ffffffUL;
+        vcpu->run->s.regs.gprs[reg1] |= (u64) status << 24;
+        if (status != 0)
+            kvm_s390_set_psw_cc(vcpu, 1);
+        else
+            kvm_s390_set_psw_cc(vcpu, 3);
+        break;
+    }
+
+    return 0;
+}
+
  #define SSKE_NQ 0x8
  #define SSKE_MR 0x4
  #define SSKE_MC 0x2
@@ -1275,6 +1319,8 @@ int kvm_s390_handle_b9(struct kvm_vcpu *vcpu)
          return handle_essa(vcpu);
      case 0xaf:
          return handle_pfmf(vcpu);
+    case 0xd3:
+        return handle_rpcit(vcpu);
      default:
          return -EOPNOTSUPP;
      }




--
Pierre Morel
IBM Lab Boeblingen



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