KVM: arm64: Upgrade VMID accesses to {READ,WRITE}_ONCE

Since TLB invalidation can run in parallel with VMID allocation,
we need to be careful and avoid any sort of load/store tearing.
Use {READ,WRITE}_ONCE consistently to avoid any surprise.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Jade Alglave <jade.alglave@arm.com>
Cc: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Signed-off-by: NMarc Zyngier <maz@kernel.org>
Signed-off-by: NWill Deacon <will@kernel.org>
Reviewed-by: NQuentin Perret <qperret@google.com>
Link: https://lore.kernel.org/r/20210806113109.2475-6-will@kernel.org

arch/arm64/include/asm/kvm_mmu.h

@@ -252,6 +252,11 @@ static inline int kvm_write_guest_lock(struct kvm *kvm, gpa_t gpa,
 
 #define kvm_phys_to_vttbr(addr)		phys_to_ttbr(addr)
 
+/*
+ * When this is (directly or indirectly) used on the TLB invalidation
+ * path, we rely on a previously issued DSB so that page table updates
+ * and VMID reads are correctly ordered.
+ */
 static __always_inline u64 kvm_get_vttbr(struct kvm_s2_mmu *mmu)
 {
 	struct kvm_vmid *vmid = &mmu->vmid;
@@ -259,7 +264,7 @@ static __always_inline u64 kvm_get_vttbr(struct kvm_s2_mmu *mmu)
 	u64 cnp = system_supports_cnp() ? VTTBR_CNP_BIT : 0;
 
 	baddr = mmu->pgd_phys;
-	vmid_field = (u64)vmid->vmid << VTTBR_VMID_SHIFT;
+	vmid_field = (u64)READ_ONCE(vmid->vmid) << VTTBR_VMID_SHIFT;
 	return kvm_phys_to_vttbr(baddr) | vmid_field | cnp;
 }
 

arch/arm64/kvm/arm.c

@@ -571,7 +571,7 @@ static void update_vmid(struct kvm_vmid *vmid)
 		kvm_call_hyp(__kvm_flush_vm_context);
 	}
 
-	vmid->vmid = kvm_next_vmid;
+	WRITE_ONCE(vmid->vmid, kvm_next_vmid);
 	kvm_next_vmid++;
 	kvm_next_vmid &= (1 << kvm_get_vmid_bits()) - 1;
 

arch/arm64/kvm/hyp/nvhe/mem_protect.c

@@ -109,8 +109,8 @@ int kvm_host_prepare_stage2(void *pgt_pool_base)
 	mmu->pgd_phys = __hyp_pa(host_kvm.pgt.pgd);
 	mmu->arch = &host_kvm.arch;
 	mmu->pgt = &host_kvm.pgt;
-	mmu->vmid.vmid_gen = 0;
-	mmu->vmid.vmid = 0;
+	WRITE_ONCE(mmu->vmid.vmid_gen, 0);
+	WRITE_ONCE(mmu->vmid.vmid, 0);
 
 	return 0;
 }

arch/arm64/kvm/mmu.c

@@ -485,7 +485,7 @@ int kvm_init_stage2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu)
 	mmu->arch = &kvm->arch;
 	mmu->pgt = pgt;
 	mmu->pgd_phys = __pa(pgt->pgd);
-	mmu->vmid.vmid_gen = 0;
+	WRITE_ONCE(mmu->vmid.vmid_gen, 0);
 	return 0;
 
 out_destroy_pgtable: