linux-kernel - [PATCH 1/2] KVM: x86: Remove misleading DR6/DR7 adjustments from RSM emulation

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Date:   Thu,  4 Feb 2021 17:24:57 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] KVM: x86: Remove misleading DR6/DR7 adjustments from RSM emulation

Drop the DR6/7 volatile+fixed bits adjustments in RSM emulation, which
are redundant and misleading.  The necessary adjustments are made by
kvm_set_dr(), which properly sets the fixed bits that are conditional
on the vCPU model.

Note, KVM incorrectly reads only bits 31:0 of the DR6/7 fields when
emulating RSM on x86-64.  On the plus side for this change, that bug
makes removing "& DRx_VOLATILE" a nop.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/emulate.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 9641cff06722..2e6e6c39922f 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2506,12 +2506,12 @@ static int rsm_load_state_32(struct x86_emulate_ctxt *ctxt,
 
 	val = GET_SMSTATE(u32, smstate, 0x7fcc);
 
-	if (ctxt->ops->set_dr(ctxt, 6, (val & DR6_VOLATILE) | DR6_FIXED_1))
+	if (ctxt->ops->set_dr(ctxt, 6, val))
 		return X86EMUL_UNHANDLEABLE;
 
 	val = GET_SMSTATE(u32, smstate, 0x7fc8);
 
-	if (ctxt->ops->set_dr(ctxt, 7, (val & DR7_VOLATILE) | DR7_FIXED_1))
+	if (ctxt->ops->set_dr(ctxt, 7, val))
 		return X86EMUL_UNHANDLEABLE;
 
 	selector =                 GET_SMSTATE(u32, smstate, 0x7fc4);
@@ -2566,12 +2566,12 @@ static int rsm_load_state_64(struct x86_emulate_ctxt *ctxt,
 
 	val = GET_SMSTATE(u32, smstate, 0x7f68);
 
-	if (ctxt->ops->set_dr(ctxt, 6, (val & DR6_VOLATILE) | DR6_FIXED_1))
+	if (ctxt->ops->set_dr(ctxt, 6, val))
 		return X86EMUL_UNHANDLEABLE;
 
 	val = GET_SMSTATE(u32, smstate, 0x7f60);
 
-	if (ctxt->ops->set_dr(ctxt, 7, (val & DR7_VOLATILE) | DR7_FIXED_1))
+	if (ctxt->ops->set_dr(ctxt, 7, val))
 		return X86EMUL_UNHANDLEABLE;
 
 	cr0 =                       GET_SMSTATE(u64, smstate, 0x7f58);
-- 
2.30.0.365.g02bc693789-goog