Re: [PATCH v3 1/3] KVM: SVM: use vmsave/vmload for saving/restoring additional host state

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On 1/7/21 9:32 AM, Tom Lendacky wrote:
On 1/5/21 11:20 AM, Sean Christopherson wrote:
On Tue, Jan 05, 2021, Michael Roth wrote:
@@ -3703,16 +3688,9 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu,
      if (sev_es_guest(svm->vcpu.kvm)) {
          __svm_sev_es_vcpu_run(svm->vmcb_pa);
      } else {
-        __svm_vcpu_run(svm->vmcb_pa, (unsigned long *)&svm->vcpu.arch.regs);
-
-#ifdef CONFIG_X86_64
-        native_wrmsrl(MSR_GS_BASE, svm->host.gs_base);
-#else
-        loadsegment(fs, svm->host.fs);
-#ifndef CONFIG_X86_32_LAZY_GS
-        loadsegment(gs, svm->host.gs);
-#endif
-#endif
+        __svm_vcpu_run(svm->vmcb_pa, (unsigned long *)&svm->vcpu.arch.regs,
+                   page_to_phys(per_cpu(svm_data,
+                            vcpu->cpu)->save_area));

Does this need to use __sme_page_pa()?

Yes, it should now. The SEV-ES support added the SME encryption bit to the MSR_VM_HSAVE_PA MSR, so we need to be consistent in how the data is read and written.

Oh, and also in svm_vcpu_load().

Thanks,
Tom

 > Thanks,
Tom


      }
      /*

...

diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
index 6feb8c08f45a..89f4e8e7bf0e 100644
--- a/arch/x86/kvm/svm/vmenter.S
+++ b/arch/x86/kvm/svm/vmenter.S
@@ -33,6 +33,7 @@
   * __svm_vcpu_run - Run a vCPU via a transition to SVM guest mode
   * @vmcb_pa:    unsigned long
   * @regs:    unsigned long * (to guest registers)
+ * @hostsa_pa:    unsigned long
   */
  SYM_FUNC_START(__svm_vcpu_run)
      push %_ASM_BP
@@ -47,6 +48,9 @@ SYM_FUNC_START(__svm_vcpu_run)
  #endif
      push %_ASM_BX
+    /* Save @hostsa_pa */
+    push %_ASM_ARG3
+
      /* Save @regs. */
      push %_ASM_ARG2
@@ -154,6 +158,12 @@ SYM_FUNC_START(__svm_vcpu_run)
      xor %r15d, %r15d
  #endif
+    /* "POP" @hostsa_pa to RAX. */
+    pop %_ASM_AX
+
+    /* Restore host user state and FS/GS base */
+    vmload %_ASM_AX

This VMLOAD needs the "handle fault on reboot" goo.  Seeing the code, I think I'd prefer to handle this in C code, especially if Paolo takes the svm_ops.h
patch[*].  Actually, I think with that patch it'd make sense to move the
existing VMSAVE+VMLOAD for the guest into svm.c, too.  And completely unrelated, the fault handling in svm/vmenter.S can be cleaned up a smidge to eliminate the
JMPs.

Paolo, what do you think about me folding these patches into my series to do the above cleanups?  And maybe sending a pull request for the end result? (I'd also like to add on a patch to use the user return MSR mechanism for MSR_TSC_AUX).

[*] https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flkml.kernel.org%2Fr%2F20201231002702.2223707-8-seanjc%40google.com&data=04%7C01%7Cthomas.lendacky%40amd.com%7Ca130e2c4b40442b8532108d8b321a57b%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637456304409010405%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=6vWmBbFFP0aOaZr31I7WDhpmzL4A%2FY%2BuzvvZrmDHpWI%3D&reserved=0

+
      pop %_ASM_BX
  #ifdef CONFIG_X86_64
--
2.25.1




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