Re: [PATCH 3/6] KVM: x86: Add dedicated emulator helper for grabbing CPUID.maxphyaddr

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On 03.03.20 09:48, Paolo Bonzini wrote:
On 02/03/20 20:57, Sean Christopherson wrote:
Add a helper to retrieve cpuid_maxphyaddr() instead of manually
calculating the value in the emulator via raw CPUID output.  In addition
to consolidating logic, this also paves the way toward simplifying
kvm_cpuid(), whose somewhat confusing return value exists purely to
support the emulator's maxphyaddr calculation.

No functional change intended.

I don't think this is a particularly useful change.  Yes, it's not
intuitive but is it more than a matter of documentation (and possibly
moving the check_cr_write snippet into a separate function)?

Besides the non obvious return value of the current function, this approach also avoids leaving cpuid traces for querying maxphyaddr, which is also not very intuitive IMHO.

Jan


Paolo

Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
---
  arch/x86/include/asm/kvm_emulate.h |  1 +
  arch/x86/kvm/emulate.c             | 10 +---------
  arch/x86/kvm/x86.c                 |  6 ++++++
  3 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
index bf5f5e476f65..ded06515d30f 100644
--- a/arch/x86/include/asm/kvm_emulate.h
+++ b/arch/x86/include/asm/kvm_emulate.h
@@ -222,6 +222,7 @@ struct x86_emulate_ops {
bool (*get_cpuid)(struct x86_emulate_ctxt *ctxt, u32 *eax, u32 *ebx,
  			  u32 *ecx, u32 *edx, bool check_limit);
+	int (*get_cpuid_maxphyaddr)(struct x86_emulate_ctxt *ctxt);
  	bool (*guest_has_long_mode)(struct x86_emulate_ctxt *ctxt);
  	bool (*guest_has_movbe)(struct x86_emulate_ctxt *ctxt);
  	bool (*guest_has_fxsr)(struct x86_emulate_ctxt *ctxt);
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index dd19fb3539e0..bf02ed51e90f 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -4244,16 +4244,8 @@ static int check_cr_write(struct x86_emulate_ctxt *ctxt)
ctxt->ops->get_msr(ctxt, MSR_EFER, &efer);
  		if (efer & EFER_LMA) {
-			u64 maxphyaddr;
-			u32 eax, ebx, ecx, edx;
+			int maxphyaddr = ctxt->ops->get_cpuid_maxphyaddr(ctxt);
- eax = 0x80000008;
-			ecx = 0;
-			if (ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx,
-						 &edx, false))
-				maxphyaddr = eax & 0xff;
-			else
-				maxphyaddr = 36;
  			rsvd = rsvd_bits(maxphyaddr, 63);
  			if (ctxt->ops->get_cr(ctxt, 4) & X86_CR4_PCIDE)
  				rsvd &= ~X86_CR3_PCID_NOFLUSH;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ddd1d296bd20..5467ee71c25b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6209,6 +6209,11 @@ static bool emulator_get_cpuid(struct x86_emulate_ctxt *ctxt,
  	return kvm_cpuid(emul_to_vcpu(ctxt), eax, ebx, ecx, edx, check_limit);
  }
+static int emulator_get_cpuid_maxphyaddr(struct x86_emulate_ctxt *ctxt)
+{
+	return cpuid_maxphyaddr(emul_to_vcpu(ctxt));
+}
+
  static bool emulator_guest_has_long_mode(struct x86_emulate_ctxt *ctxt)
  {
  	return guest_cpuid_has(emul_to_vcpu(ctxt), X86_FEATURE_LM);
@@ -6301,6 +6306,7 @@ static const struct x86_emulate_ops emulate_ops = {
  	.fix_hypercall       = emulator_fix_hypercall,
  	.intercept           = emulator_intercept,
  	.get_cpuid           = emulator_get_cpuid,
+	.get_cpuid_maxphyaddr= emulator_get_cpuid_maxphyaddr,
  	.guest_has_long_mode = emulator_guest_has_long_mode,
  	.guest_has_movbe     = emulator_guest_has_movbe,
  	.guest_has_fxsr      = emulator_guest_has_fxsr,



--
Siemens AG, Corporate Technology, CT RDA IOT SES-DE
Corporate Competence Center Embedded Linux



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