linux-kernel - [PATCH 09/19] kvm: x86: Prepare reallocation check

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Date:   Tue,  7 Dec 2021 19:03:49 -0500
From:   Yang Zhong <yang.zhong@...el.com>
To:     x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, pbonzini@...hat.com
Cc:     seanjc@...gle.com, jun.nakajima@...el.com, kevin.tian@...el.com,
        jing2.liu@...ux.intel.com, jing2.liu@...el.com,
        yang.zhong@...el.com
Subject: [PATCH 09/19] kvm: x86: Prepare reallocation check

From: Jing Liu <jing2.liu@...el.com>

On native fpstate reallocation is triggered by #NM because IA32_XFD
is initialized to 1 for all native tasks.

However #NM in guest is not trapped by KVM. Instead, guest enabling
of a dynamic extended feature can be captured via emulation of
IA32_XFD and XSETBV. Basically having guest XCR0[i]=1 and XFD[i]=0
indicates that the feature[i] is activated by the guest.

This patch provides a helper function for such check, invoked when
either XCR0 or XFD is changed in the emulation path.

Signed-off-by: Jing Liu <jing2.liu@...el.com>
Signed-off-by: Kevin Tian <kevin.tian@...el.com>
Signed-off-by: Yang Zhong <yang.zhong@...el.com>
---
 arch/x86/kvm/x86.c | 24 ++++++++++++++++++++++++
 arch/x86/kvm/x86.h |  1 +
 2 files changed, 25 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 05f2cda73d69..91cc6f69a7ca 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -956,6 +956,30 @@ void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu)
 }
 EXPORT_SYMBOL_GPL(kvm_load_host_xsave_state);
 
+bool kvm_check_guest_realloc_fpstate(struct kvm_vcpu *vcpu, u64 xfd)
+{
+	u64 xcr0 = vcpu->arch.xcr0 & XFEATURE_MASK_USER_DYNAMIC;
+
+	/* For any state which is enabled dynamically */
+	if ((xfd & xcr0) != xcr0) {
+		u64 request = (xcr0 ^ xfd) & xcr0;
+		struct fpu_guest *guest_fpu = &vcpu->arch.guest_fpu;
+
+		/*
+		 * If requested features haven't been enabled, update
+		 * the request bitmap and tell the caller to request
+		 * dynamic buffer reallocation.
+		 */
+		if ((guest_fpu->user_xfeatures & request) != request) {
+			vcpu->arch.guest_fpu.realloc_request = request;
+			return true;
+		}
+	}
+
+	return false;
+}
+EXPORT_SYMBOL_GPL(kvm_check_guest_realloc_fpstate);
+
 static int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
 {
 	u64 xcr0 = xcr;
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 4abcd8d9836d..24a323980146 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -445,6 +445,7 @@ static inline void kvm_machine_check(void)
 
 void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu);
 void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu);
+bool kvm_check_guest_realloc_fpstate(struct kvm_vcpu *vcpu, u64 new_xfd);
 int kvm_spec_ctrl_test_value(u64 value);
 bool kvm_is_valid_cr4(struct kvm_vcpu *vcpu, unsigned long cr4);
 int kvm_handle_memory_failure(struct kvm_vcpu *vcpu, int r,