linux-kernel - [PATCH 11/24] KVM: x86/mmu: Add module param to disable MMIO caching (for testing)

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Date:   Thu, 25 Feb 2021 12:47:36 -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, Ben Gardon <bgardon@...gle.com>
Subject: [PATCH 11/24] KVM: x86/mmu: Add module param to disable MMIO caching
 (for testing)

Add a module param to disable MMIO caching so that it's possible to test
the related flows without access to the necessary hardware.  Using shadow
paging with 64-bit KVM and 52 bits of physical address space must disable
MMIO caching as there are no reserved bits to be had.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/mmu/spte.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
index b2379094a8c1..503dec3f8c7a 100644
--- a/arch/x86/kvm/mmu/spte.c
+++ b/arch/x86/kvm/mmu/spte.c
@@ -17,6 +17,9 @@
 
 #include <asm/e820/api.h>
 
+static bool __read_mostly enable_mmio_caching = true;
+module_param_named(mmio_caching, enable_mmio_caching, bool, 0444);
+
 u64 __read_mostly shadow_nx_mask;
 u64 __read_mostly shadow_x_mask; /* mutual exclusive with nx_mask */
 u64 __read_mostly shadow_user_mask;
@@ -251,6 +254,9 @@ void kvm_mmu_set_mmio_spte_mask(u64 mmio_value, u64 mmio_mask, u64 access_mask)
 	BUG_ON((u64)(unsigned)access_mask != access_mask);
 	WARN_ON(mmio_value & shadow_nonpresent_or_rsvd_lower_gfn_mask);
 
+	if (!enable_mmio_caching)
+		mmio_value = 0;
+
 	/*
 	 * Disable MMIO caching if the MMIO value collides with the bits that
 	 * are used to hold the relocated GFN when the L1TF mitigation is
-- 
2.30.1.766.gb4fecdf3b7-goog