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Subject[PATCH v2 09/17] KVM: arm64: Support page-not-present notification
Date
The requested page might be not resident in memory during the stage-2
page fault. For example, the requested page could be resident in swap
device (file). In this case, disk I/O is issued in order to fetch the
requested page and it could take tens of milliseconds, even hundreds
of milliseconds in extreme situation. During the period, the guest's
vCPU is suspended until the requested page becomes ready. Actually,
the something else on the guest's vCPU could be rescheduled during
the period, so that the time slice isn't wasted as the guest's vCPU
can see. This is the primary goal of the feature (Asynchronous Page
Fault).

This supports delivery of page-not-present notification through SDEI
event when the requested page isn't present. When the notification is
received on the guest's vCPU, something else (another process) can be
scheduled. The design is highlighted as below:

* There is dedicated memory region shared by host and guest. It's
represented by "struct kvm_vcpu_pv_apf_data". The field @reason
indicates the reason why the SDEI event is triggered, while the
unique @token is used by guest to associate the event with the
suspended process.

* One control block is associated with each guest's vCPU and it's
represented by "struct kvm_arch_async_pf_control". It allows the
guest to configure the functionality to indicate the situations
where the host can deliver the page-not-present notification to
kick off asyncrhonous page fault. Besides, runtime states are
also maintained in this struct.

* Before the page-not-present notification is sent to the guest's
vCPU, a worker is started and executed asynchronously on host,
to fetch the requested page. "struct kvm{_,_arch}async_pf" is
associated with the worker, to track the work.

The feature isn't enabled by CONFIG_KVM_ASYNC_PF yet. Also, the
page-ready notification delivery and control path isn't implemented
and will be done in the subsequent patches.

Signed-off-by: Gavin Shan <gshan@redhat.com>
---
arch/arm64/include/asm/kvm_host.h | 50 +++++++++
arch/arm64/include/uapi/asm/kvm_para.h | 15 +++
arch/arm64/kvm/Makefile | 1 +
arch/arm64/kvm/arm.c | 3 +
arch/arm64/kvm/async_pf.c | 145 +++++++++++++++++++++++++
arch/arm64/kvm/mmu.c | 32 +++++-
6 files changed, 245 insertions(+), 1 deletion(-)
create mode 100644 arch/arm64/kvm/async_pf.c

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 00b30b7554e5..49cccefb22cf 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -273,6 +273,31 @@ struct vcpu_reset_state {
bool reset;
};

+/* Should be a power of two number */
+#define ASYNC_PF_PER_VCPU 64
+
+/*
+ * The association of gfn and token. The token will be sent to guest as
+ * page fault address. Also, the guest could be in aarch32 mode. So its
+ * length should be 32-bits.
+ */
+struct kvm_arch_async_pf {
+ u32 token;
+ gfn_t gfn;
+ u32 esr;
+};
+
+struct kvm_arch_async_pf_control {
+ struct gfn_to_hva_cache cache;
+ u64 control_block;
+ bool send_user_only;
+ u64 sdei_event_num;
+
+ u16 id;
+ bool notpresent_pending;
+ u32 notpresent_token;
+};
+
struct kvm_vcpu_arch {
struct kvm_cpu_context ctxt;
void *sve_state;
@@ -375,6 +400,7 @@ struct kvm_vcpu_arch {
} steal;

struct kvm_sdei_vcpu *sdei;
+ struct kvm_arch_async_pf_control *apf;
};

/* Pointer to the vcpu's SVE FFR for sve_{save,load}_state() */
@@ -734,6 +760,30 @@ int kvm_arm_vcpu_arch_get_attr(struct kvm_vcpu *vcpu,
int kvm_arm_vcpu_arch_has_attr(struct kvm_vcpu *vcpu,
struct kvm_device_attr *attr);

+#ifdef CONFIG_KVM_ASYNC_PF
+void kvm_arch_async_pf_create_vcpu(struct kvm_vcpu *vcpu);
+bool kvm_arch_async_not_present_allowed(struct kvm_vcpu *vcpu);
+bool kvm_arch_setup_async_pf(struct kvm_vcpu *vcpu,
+ u32 esr, gpa_t gpa, gfn_t gfn);
+bool kvm_arch_async_page_not_present(struct kvm_vcpu *vcpu,
+ struct kvm_async_pf *work);
+void kvm_arch_async_pf_destroy_vcpu(struct kvm_vcpu *vcpu);
+#else
+static inline void kvm_arch_async_pf_create_vcpu(struct kvm_vcpu *vcpu) { }
+static inline void kvm_arch_async_pf_destroy_vcpu(struct kvm_vcpu *vcpu) { }
+
+static inline bool kvm_arch_async_not_present_allowed(struct kvm_vcpu *vcpu)
+{
+ return false;
+}
+
+static inline bool kvm_arch_setup_async_pf(struct kvm_vcpu *vcpu,
+ u32 esr, gpa_t gpa, gfn_t gfn)
+{
+ return false;
+}
+#endif
+
/* Guest/host FPSIMD coordination helpers */
int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu);
void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu);
diff --git a/arch/arm64/include/uapi/asm/kvm_para.h b/arch/arm64/include/uapi/asm/kvm_para.h
index cd212282b90c..3fa04006714e 100644
--- a/arch/arm64/include/uapi/asm/kvm_para.h
+++ b/arch/arm64/include/uapi/asm/kvm_para.h
@@ -2,4 +2,19 @@
#ifndef _UAPI_ASM_ARM_KVM_PARA_H
#define _UAPI_ASM_ARM_KVM_PARA_H

+#include <linux/types.h>
+
+/* Async PF */
+#define KVM_ASYNC_PF_ENABLED (1 << 0)
+#define KVM_ASYNC_PF_SEND_ALWAYS (1 << 1)
+
+#define KVM_PV_REASON_PAGE_NOT_PRESENT 1
+
+struct kvm_vcpu_pv_apf_data {
+ __u32 reason;
+ __u32 token;
+ __u8 pad[56];
+ __u32 enabled;
+};
+
#endif /* _UAPI_ASM_ARM_KVM_PARA_H */
diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
index dcb353f29d20..35721f9076d8 100644
--- a/arch/arm64/kvm/Makefile
+++ b/arch/arm64/kvm/Makefile
@@ -25,3 +25,4 @@ kvm-y := $(KVM)/kvm_main.o $(KVM)/coalesced_mmio.o $(KVM)/eventfd.o \
vgic/vgic-its.o vgic/vgic-debug.o

kvm-$(CONFIG_HW_PERF_EVENTS) += pmu-emul.o
+kvm-$(CONFIG_KVM_ASYNC_PF) += $(KVM)/async_pf.o async_pf.o
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index f8b44a29e164..c98fbb4e914b 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -330,6 +330,8 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)

kvm_sdei_create_vcpu(vcpu);

+ kvm_arch_async_pf_create_vcpu(vcpu);
+
vcpu->arch.hw_mmu = &vcpu->kvm->arch.mmu;

err = kvm_vgic_vcpu_init(vcpu);
@@ -351,6 +353,7 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
kvm_mmu_free_memory_cache(&vcpu->arch.mmu_page_cache);
kvm_timer_vcpu_terminate(vcpu);
kvm_pmu_vcpu_destroy(vcpu);
+ kvm_arch_async_pf_destroy_vcpu(vcpu);
kvm_sdei_destroy_vcpu(vcpu);

kvm_arm_vcpu_destroy(vcpu);
diff --git a/arch/arm64/kvm/async_pf.c b/arch/arm64/kvm/async_pf.c
new file mode 100644
index 000000000000..742bb8a0a8c0
--- /dev/null
+++ b/arch/arm64/kvm/async_pf.c
@@ -0,0 +1,145 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Asynchronous page fault support.
+ *
+ * Copyright (C) 2021 Red Hat, Inc.
+ *
+ * Author(s): Gavin Shan <gshan@redhat.com>
+ */
+
+#include <linux/arm-smccc.h>
+#include <linux/kvm_host.h>
+#include <asm/kvm_emulate.h>
+#include <kvm/arm_hypercalls.h>
+#include <kvm/arm_vgic.h>
+#include <asm/kvm_sdei.h>
+
+static inline int read_cache(struct kvm_vcpu *vcpu, u32 offset, u32 *val)
+{
+ struct kvm *kvm = vcpu->kvm;
+ struct kvm_arch_async_pf_control *apf = vcpu->arch.apf;
+
+ return kvm_read_guest_offset_cached(kvm, &apf->cache,
+ val, offset, sizeof(*val));
+}
+
+static inline int write_cache(struct kvm_vcpu *vcpu, u32 offset, u32 val)
+{
+ struct kvm *kvm = vcpu->kvm;
+ struct kvm_arch_async_pf_control *apf = vcpu->arch.apf;
+
+ return kvm_write_guest_offset_cached(kvm, &apf->cache,
+ &val, offset, sizeof(val));
+}
+
+void kvm_arch_async_pf_create_vcpu(struct kvm_vcpu *vcpu)
+{
+ vcpu->arch.apf = kzalloc(sizeof(*(vcpu->arch.apf)), GFP_KERNEL);
+}
+
+bool kvm_arch_async_not_present_allowed(struct kvm_vcpu *vcpu)
+{
+ struct kvm *kvm = vcpu->kvm;
+ struct kvm_arch_async_pf_control *apf = vcpu->arch.apf;
+ struct kvm_sdei_vcpu *vsdei = vcpu->arch.sdei;
+ u32 reason, token;
+ int ret;
+
+ if (!apf || !(apf->control_block & KVM_ASYNC_PF_ENABLED))
+ return false;
+
+ if (apf->send_user_only && vcpu_mode_priv(vcpu))
+ return false;
+
+ if (!irqchip_in_kernel(vcpu->kvm))
+ return false;
+
+ if (!vsdei || vsdei->critical_event || vsdei->normal_event)
+ return false;
+
+ /* Pending page fault, which isn't acknowledged by guest */
+ ret = read_cache(vcpu, offsetof(struct kvm_vcpu_pv_apf_data, reason),
+ &reason);
+ if (ret) {
+ kvm_err("%s: Error %d to read reason (%d-%d)\n",
+ __func__, ret, kvm->userspace_pid, vcpu->vcpu_idx);
+ return false;
+ }
+
+ ret = read_cache(vcpu, offsetof(struct kvm_vcpu_pv_apf_data, token),
+ &token);
+ if (ret) {
+ kvm_err("%s: Error %d to read token %d-%d\n",
+ __func__, ret, kvm->userspace_pid, vcpu->vcpu_idx);
+ return false;
+ }
+
+ if (reason || token)
+ return false;
+
+ return true;
+}
+
+bool kvm_arch_setup_async_pf(struct kvm_vcpu *vcpu,
+ u32 esr, gpa_t gpa, gfn_t gfn)
+{
+ struct kvm_arch_async_pf_control *apf = vcpu->arch.apf;
+ struct kvm_arch_async_pf arch;
+ unsigned long hva = kvm_vcpu_gfn_to_hva(vcpu, gfn);
+
+ arch.token = (apf->id++ << 12) | vcpu->vcpu_id;
+ arch.gfn = gfn;
+ arch.esr = esr;
+
+ return kvm_setup_async_pf(vcpu, gpa, hva, &arch);
+}
+
+/*
+ * It's guaranteed that no pending asynchronous page fault when this is
+ * called. It means all previous issued asynchronous page faults have
+ * been acknowledged.
+ */
+bool kvm_arch_async_page_not_present(struct kvm_vcpu *vcpu,
+ struct kvm_async_pf *work)
+{
+ struct kvm *kvm = vcpu->kvm;
+ struct kvm_arch_async_pf_control *apf = vcpu->arch.apf;
+ int ret;
+
+ kvm_async_pf_add_slot(vcpu, work->arch.gfn);
+
+ ret = write_cache(vcpu, offsetof(struct kvm_vcpu_pv_apf_data, token),
+ work->arch.token);
+ if (ret) {
+ kvm_err("%s: Error %d to write token (%d-%d %08x)\n",
+ __func__, ret, kvm->userspace_pid,
+ vcpu->vcpu_idx, work->arch.token);
+ goto fail;
+ }
+
+ ret = write_cache(vcpu, offsetof(struct kvm_vcpu_pv_apf_data, reason),
+ KVM_PV_REASON_PAGE_NOT_PRESENT);
+ if (ret) {
+ kvm_err("%s: Error %d to write reason (%d-%d %08x)\n",
+ __func__, ret, kvm->userspace_pid,
+ vcpu->vcpu_idx, work->arch.token);
+ goto fail;
+ }
+
+ apf->notpresent_pending = true;
+ apf->notpresent_token = work->arch.token;
+
+ return !kvm_sdei_inject(vcpu, apf->sdei_event_num, true);
+
+fail:
+ write_cache(vcpu, offsetof(struct kvm_vcpu_pv_apf_data, token), 0);
+ write_cache(vcpu, offsetof(struct kvm_vcpu_pv_apf_data, reason), 0);
+ kvm_async_pf_remove_slot(vcpu, work->arch.gfn);
+ return false;
+}
+
+void kvm_arch_async_pf_destroy_vcpu(struct kvm_vcpu *vcpu)
+{
+ kfree(vcpu->arch.apf);
+ vcpu->arch.apf = NULL;
+}
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index ff8480b68fb8..f170c44691f0 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -760,6 +760,33 @@ static inline bool is_write_fault(unsigned int esr)
return esr_dabt_is_wnr(esr);
}

+static bool try_async_pf(struct kvm_vcpu *vcpu, u32 esr, gpa_t gpa,
+ gfn_t gfn, kvm_pfn_t *pfn, bool write,
+ bool *writable, bool prefault)
+{
+ struct kvm_arch_async_pf_control *apf = vcpu->arch.apf;
+ struct kvm_memory_slot *slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
+ bool async = false;
+
+ if (apf) {
+ /* Bail if *pfn has correct page */
+ *pfn = __gfn_to_pfn_memslot(slot, gfn, false,
+ &async, write, writable);
+ if (!async)
+ return false;
+
+ if (!prefault && kvm_arch_async_not_present_allowed(vcpu)) {
+ if (kvm_async_pf_find_slot(vcpu, gfn) ||
+ kvm_arch_setup_async_pf(vcpu, esr, gpa, gfn))
+ return true;
+ }
+ }
+
+ *pfn = __gfn_to_pfn_memslot(slot, gfn, false,
+ NULL, write, writable);
+ return false;
+}
+
int kvm_handle_user_mem_abort(struct kvm_vcpu *vcpu,
struct kvm_memory_slot *memslot,
phys_addr_t fault_ipa,
@@ -871,7 +898,10 @@ int kvm_handle_user_mem_abort(struct kvm_vcpu *vcpu,
*/
smp_rmb();

- pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, &writable);
+ if (try_async_pf(vcpu, esr, fault_ipa, gfn, &pfn,
+ write_fault, &writable, prefault))
+ return 1;
+
if (pfn == KVM_PFN_ERR_HWPOISON) {
kvm_send_hwpoison_signal(hva, vma_shift);
return 0;
--
2.23.0
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