From 1880afd6057f34586919715e8ffe9c5858f4a326 Mon Sep 17 00:00:00 2001 From: James Hogan Date: Mon, 28 Nov 2016 23:04:52 +0000 Subject: [PATCH] KVM: MIPS/T&E: Add lockless GVA access helpers MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Add helpers to allow for lockless direct access to the GVA space, by changing the VCPU mode to READING_SHADOW_PAGE_TABLES for the duration of the access. This allows asynchronous TLB flush requests in future patches to safely trigger either a TLB flush before the direct GVA space access, or a delay until the in-progress lockless direct access is complete. The kvm_trap_emul_gva_lockless_begin() and kvm_trap_emul_gva_lockless_end() helpers take care of guarding the direct GVA accesses, and kvm_trap_emul_gva_fault() tries to handle a uaccess fault resulting from a flush having taken place. Signed-off-by: James Hogan Cc: Paolo Bonzini Cc: "Radim Krčmář" Cc: Ralf Baechle Cc: linux-mips@linux-mips.org Cc: kvm@vger.kernel.org --- arch/mips/include/asm/kvm_host.h | 15 ++++++++++ arch/mips/kvm/mmu.c | 51 +++++++++++++++++++++++++++++++ arch/mips/kvm/trap_emul.c | 65 ++++++++++++++++++++++++++++++++++++++++ 3 files changed, 131 insertions(+) diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h index a046579..c1e46ab 100644 --- a/arch/mips/include/asm/kvm_host.h +++ b/arch/mips/include/asm/kvm_host.h @@ -243,6 +243,7 @@ enum emulation_result { #define TLB_ASID(x) ((x).tlb_hi & KVM_ENTRYHI_ASID) #define TLB_LO_IDX(x, va) (((va) >> PAGE_SHIFT) & 1) #define TLB_IS_VALID(x, va) ((x).tlb_lo[TLB_LO_IDX(x, va)] & ENTRYLO_V) +#define TLB_IS_DIRTY(x, va) ((x).tlb_lo[TLB_LO_IDX(x, va)] & ENTRYLO_D) #define TLB_HI_VPN2_HIT(x, y) ((TLB_VPN2(x) & ~(x).tlb_mask) == \ ((y) & VPN2_MASK & ~(x).tlb_mask)) #define TLB_HI_ASID_HIT(x, y) (TLB_IS_GLOBAL(x) || \ @@ -640,6 +641,20 @@ pgd_t *kvm_pgd_alloc(void); void kvm_mmu_free_memory_caches(struct kvm_vcpu *vcpu); void kvm_trap_emul_invalidate_gva(struct kvm_vcpu *vcpu, unsigned long addr, bool user); +void kvm_trap_emul_gva_lockless_begin(struct kvm_vcpu *vcpu); +void kvm_trap_emul_gva_lockless_end(struct kvm_vcpu *vcpu); + +enum kvm_mips_fault_result { + KVM_MIPS_MAPPED = 0, + KVM_MIPS_GVA, + KVM_MIPS_GPA, + KVM_MIPS_TLB, + KVM_MIPS_TLBINV, + KVM_MIPS_TLBMOD, +}; +enum kvm_mips_fault_result kvm_trap_emul_gva_fault(struct kvm_vcpu *vcpu, + unsigned long gva, + bool write); /* Emulation */ int kvm_get_inst(u32 *opc, struct kvm_vcpu *vcpu, u32 *out); diff --git a/arch/mips/kvm/mmu.c b/arch/mips/kvm/mmu.c index e41ee36..32c317d 100644 --- a/arch/mips/kvm/mmu.c +++ b/arch/mips/kvm/mmu.c @@ -732,6 +732,57 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu) local_irq_restore(flags); } +/** + * kvm_trap_emul_gva_fault() - Safely attempt to handle a GVA access fault. + * @vcpu: Virtual CPU. + * @gva: Guest virtual address to be accessed. + * @write: True if write attempted (must be dirtied and made writable). + * + * Safely attempt to handle a GVA fault, mapping GVA pages if necessary, and + * dirtying the page if @write so that guest instructions can be modified. + * + * Returns: KVM_MIPS_MAPPED on success. + * KVM_MIPS_GVA if bad guest virtual address. + * KVM_MIPS_GPA if bad guest physical address. + * KVM_MIPS_TLB if guest TLB not present. + * KVM_MIPS_TLBINV if guest TLB present but not valid. + * KVM_MIPS_TLBMOD if guest TLB read only. + */ +enum kvm_mips_fault_result kvm_trap_emul_gva_fault(struct kvm_vcpu *vcpu, + unsigned long gva, + bool write) +{ + struct mips_coproc *cop0 = vcpu->arch.cop0; + struct kvm_mips_tlb *tlb; + int index; + + if (KVM_GUEST_KSEGX(gva) == KVM_GUEST_KSEG0) { + if (kvm_mips_handle_kseg0_tlb_fault(gva, vcpu) < 0) + return KVM_MIPS_GPA; + } else if ((KVM_GUEST_KSEGX(gva) < KVM_GUEST_KSEG0) || + KVM_GUEST_KSEGX(gva) == KVM_GUEST_KSEG23) { + /* Address should be in the guest TLB */ + index = kvm_mips_guest_tlb_lookup(vcpu, (gva & VPN2_MASK) | + (kvm_read_c0_guest_entryhi(cop0) & KVM_ENTRYHI_ASID)); + if (index < 0) + return KVM_MIPS_TLB; + tlb = &vcpu->arch.guest_tlb[index]; + + /* Entry should be valid, and dirty for writes */ + if (!TLB_IS_VALID(*tlb, gva)) + return KVM_MIPS_TLBINV; + if (write && !TLB_IS_DIRTY(*tlb, gva)) + return KVM_MIPS_TLBMOD; + + if (kvm_mips_handle_mapped_seg_tlb_fault(vcpu, tlb, gva)) + return KVM_MIPS_GPA; + } else { + return KVM_MIPS_GVA; + } + + return KVM_MIPS_MAPPED; +} + int kvm_get_inst(u32 *opc, struct kvm_vcpu *vcpu, u32 *out) { int err; diff --git a/arch/mips/kvm/trap_emul.c b/arch/mips/kvm/trap_emul.c index edda8f0..e20369d 100644 --- a/arch/mips/kvm/trap_emul.c +++ b/arch/mips/kvm/trap_emul.c @@ -786,6 +786,71 @@ static void kvm_trap_emul_check_requests(struct kvm_vcpu *vcpu, int cpu, } } +/** + * kvm_trap_emul_gva_lockless_begin() - Begin lockless access to GVA space. + * @vcpu: VCPU pointer. + * + * Call before a GVA space access outside of guest mode, to ensure that + * asynchronous TLB flush requests are handled or delayed until completion of + * the GVA access (as indicated by a matching kvm_trap_emul_gva_lockless_end()). + * + * Should be called with IRQs already enabled. + */ +void kvm_trap_emul_gva_lockless_begin(struct kvm_vcpu *vcpu) +{ + /* We re-enable IRQs in kvm_trap_emul_gva_lockless_end() */ + WARN_ON_ONCE(irqs_disabled()); + + /* + * The caller is about to access the GVA space, so we set the mode to + * force TLB flush requests to send an IPI, and also disable IRQs to + * delay IPI handling until kvm_trap_emul_gva_lockless_end(). + */ + local_irq_disable(); + + /* + * Make sure the read of VCPU requests is not reordered ahead of the + * write to vcpu->mode, or we could miss a TLB flush request while + * the requester sees the VCPU as outside of guest mode and not needing + * an IPI. + */ + smp_store_mb(vcpu->mode, READING_SHADOW_PAGE_TABLES); + + /* + * If a TLB flush has been requested (potentially while + * OUTSIDE_GUEST_MODE and assumed immediately effective), perform it + * before accessing the GVA space, and be sure to reload the ASID if + * necessary as it'll be immediately used. + * + * TLB flush requests after this check will trigger an IPI due to the + * mode change above, which will be delayed due to IRQs disabled. + */ + kvm_trap_emul_check_requests(vcpu, smp_processor_id(), true); +} + +/** + * kvm_trap_emul_gva_lockless_end() - End lockless access to GVA space. + * @vcpu: VCPU pointer. + * + * Called after a GVA space access outside of guest mode. Should have a matching + * call to kvm_trap_emul_gva_lockless_begin(). + */ +void kvm_trap_emul_gva_lockless_end(struct kvm_vcpu *vcpu) +{ + /* + * Make sure the write to vcpu->mode is not reordered in front of GVA + * accesses, or a TLB flush requester may not think it necessary to send + * an IPI. + */ + smp_store_release(&vcpu->mode, OUTSIDE_GUEST_MODE); + + /* + * Now that the access to GVA space is complete, its safe for pending + * TLB flush request IPIs to be handled (which indicates completion). + */ + local_irq_enable(); +} + static void kvm_trap_emul_vcpu_reenter(struct kvm_run *run, struct kvm_vcpu *vcpu) { -- 2.7.4