[PATCH v2] KVM: x86: Sync the states size with the XCR0/IA32_XSS at any time

[Like Xu <like.xu.linux@gmail.com>]

From: Like Xu <likexu@tencent.com>

XCR0 is reset to 1 by RESET but not INIT and IA32_XSS is zeroed by
both RESET and INIT. The kvm_set_msr_common()'s handling of MSR_IA32_XSS
also needs to update kvm_update_cpuid_runtime(). In the above cases, the
size in bytes of the XSAVE area containing all states enabled by XCR0 or
(XCRO | IA32_XSS) needs to be updated.

For simplicity and consistency, legacy helpers are used to write values
and call kvm_update_cpuid_runtime(), and it's not exactly a fast path.

Fixes: a554d207dc46 ("KVM: X86: Processor States following Reset or INIT")
Signed-off-by: Like Xu <likexu@tencent.com>
---
v1 -> v2 Changelog:
- Strongly prefer that use the helpers to write the values; (Sean)
- Postpone IA32_XSS test cases once non-zero values are supported; (Paolo)
- User space may call SET_CPUID2 after kvm_vcpu_reset(init_event=false); (Paolo)

  arch/x86/kvm/x86.c | 4 ++--
  1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 55518b7d3b96..22d4b1d15e94 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11256,7 +11256,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)

  		vcpu->arch.msr_misc_features_enables = 0;

-		vcpu->arch.xcr0 = XFEATURE_MASK_FP;
+		__kvm_set_xcr(vcpu, 0, XFEATURE_MASK_FP);
  	}

  	/* All GPRs except RDX (handled below) are zeroed on RESET/INIT. */
@@ -11273,7 +11273,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
  	cpuid_0x1 = kvm_find_cpuid_entry(vcpu, 1, 0);
  	kvm_rdx_write(vcpu, cpuid_0x1 ? cpuid_0x1->eax : 0x600);

-	vcpu->arch.ia32_xss = 0;
+	__kvm_set_msr(vcpu, MSR_IA32_XSS, 0, true);

  	static_call(kvm_x86_vcpu_reset)(vcpu, init_event);

-- 
2.33.1