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Subject[PATCH v2 30/32] KVM: x86/mmu: Add module param to force TLB flush on root reuse
Date
Add a module param, flush_on_reuse, to override skip_tlb_flush when
performing a so called "fast cr3 switch", i.e. when reusing a cached
root. The primary motiviation for the control is to provide a fallback
mechanism in the event that TLB flushing bugs are exposed/introduced by
upcoming changes to stop unconditionally flushing on nested VMX
transitions.

Suggested-by: Jim Mattson <jmattson@google.com>
Suggested-by: Junaid Shahid <junaids@google.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/kvm/mmu/mmu.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 97d906a42e81..b98482b60748 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -78,6 +78,9 @@ module_param_cb(nx_huge_pages_recovery_ratio, &nx_huge_pages_recovery_ratio_ops,
&nx_huge_pages_recovery_ratio, 0644);
__MODULE_PARM_TYPE(nx_huge_pages_recovery_ratio, "uint");

+static bool __read_mostly force_tlb_flush_on_reuse;
+module_param_named(flush_on_reuse, force_tlb_flush_on_reuse, bool, 0644);
+
/*
* When setting this variable to true it enables Two-Dimensional-Paging
* where the hardware walks 2 page tables:
@@ -4340,6 +4343,9 @@ static void __kvm_mmu_new_cr3(struct kvm_vcpu *vcpu, gpa_t new_cr3,
union kvm_mmu_page_role new_role,
bool skip_tlb_flush)
{
+ if (force_tlb_flush_on_reuse)
+ skip_tlb_flush = false;
+
if (!fast_cr3_switch(vcpu, new_cr3, new_role, skip_tlb_flush))
kvm_mmu_free_roots(vcpu, vcpu->arch.mmu,
KVM_MMU_ROOT_CURRENT);
--
2.24.1
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