[PATCH v7 06/12] Add PV MSR to enable asynchronous page faults delivery.

Gleb Natapov
2010-10-14T09:22:50Z

Guest enables async PF vcpu functionality using this MSR.

Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
---
Documentation/kvm/cpuid.txt | 3 +++
Documentation/kvm/msr.txt | 36 +++++++++++++++++++++++++++++++++++-
arch/x86/include/asm/kvm_host.h | 2 ++
arch/x86/include/asm/kvm_para.h | 4 ++++
arch/x86/kvm/x86.c | 38 ++++++++++++++++++++++++++++++++++++--
include/linux/kvm.h | 1 +
include/linux/kvm_host.h | 1 +
virt/kvm/async_pf.c | 20 ++++++++++++++++++++
8 files changed, 102 insertions(+), 3 deletions(-)

diff --git a/Documentation/kvm/cpuid.txt b/Documentation/kvm/cpuid.txt
index 14a12ea..8820685 100644
--- a/Documentation/kvm/cpuid.txt
+++ b/Documentation/kvm/cpuid.txt
@@ -36,6 +36,9 @@ KVM_FEATURE_MMU_OP || 2 || deprecated.
KVM_FEATURE_CLOCKSOURCE2 || 3 || kvmclock available at msrs
|| || 0x4b564d00 and 0x4b564d01
------------------------------------------------------------------------------
+KVM_FEATURE_ASYNC_PF || 4 || async pf can be enabled by
+ || || writing to msr 0x4b564d02
+------------------------------------------------------------------------------
KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side
|| || per-cpu warps are expected in
|| || kvmclock.
diff --git a/Documentation/kvm/msr.txt b/Documentation/kvm/msr.txt
index 8ddcfe8..27c11a6 100644
--- a/Documentation/kvm/msr.txt
+++ b/Documentation/kvm/msr.txt
@@ -3,7 +3,6 @@ Glauber Costa <glommer@redhat.com>, Red Hat Inc, 2010
=====================================================

KVM makes use of some custom MSRs to service some requests.
-At present, this facility is only used by kvmclock.

Custom MSRs have a range reserved for them, that goes from
0x4b564d00 to 0x4b564dff. There are MSRs outside this area,
@@ -151,3 +150,38 @@ MSR_KVM_SYSTEM_TIME: 0x12
return PRESENT;
} else
return NON_PRESENT;
+
+MSR_KVM_ASYNC_PF_EN: 0x4b564d02
+ data: Bits 63-6 hold 64-byte aligned physical address of a
+ 64 byte memory area which must be in guest RAM and must be
+ zeroed. Bits 5-1 are reserved and should be zero. Bit 0 is 1
+ when asynchronous page faults are enabled on the vcpu 0 when
+ disabled.
+
+ First 4 byte of 64 byte memory location will be written to by
+ the hypervisor at the time of asynchronous page fault (APF)
+ injection to indicate type of asynchronous page fault. Value
+ of 1 means that the page referred to by the page fault is not
+ present. Value 2 means that the page is now available. Disabling
+ interrupt inhibits APFs. Guest must not enable interrupt
+ before the reason is read, or it may be overwritten by another
+ APF. Since APF uses the same exception vector as regular page
+ fault guest must reset the reason to 0 before it does
+ something that can generate normal page fault. If during page
+ fault APF reason is 0 it means that this is regular page
+ fault.
+
+ During delivery of type 1 APF cr2 contains a token that will
+ be used to notify a guest when missing page becomes
+ available. When page becomes available type 2 APF is sent with
+ cr2 set to the token associated with the page. There is special
+ kind of token 0xffffffff which tells vcpu that it should wake
+ up all processes waiting for APFs and no individual type 2 APFs
+ will be sent.
+
+ If APF is disabled while there are outstanding APFs, they will
+ not be delivered.
+
+ Currently type 2 APF will be always delivered on the same vcpu as
+ type 1 was, but guest should not rely on that.
+
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 96aca44..26b2064 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -419,6 +419,8 @@ struct kvm_vcpu_arch {
struct {
bool halted;
gfn_t gfns[roundup_pow_of_two(ASYNC_PF_PER_VCPU)];
+ struct gfn_to_hva_cache data;
+ u64 msr_val;
} apf;
};

diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
index e3faaaf..8662ae0 100644
--- a/arch/x86/include/asm/kvm_para.h
+++ b/arch/x86/include/asm/kvm_para.h
@@ -20,6 +20,7 @@
* are available. The use of 0x11 and 0x12 is deprecated
*/
#define KVM_FEATURE_CLOCKSOURCE2 3
+#define KVM_FEATURE_ASYNC_PF 4

/* The last 8 bits are used to indicate how to interpret the flags field
* in pvclock structure. If no bits are set, all flags are ignored.
@@ -32,9 +33,12 @@
/* Custom MSRs falls in the range 0x4b564d00-0x4b564dff */
#define MSR_KVM_WALL_CLOCK_NEW 0x4b564d00
#define MSR_KVM_SYSTEM_TIME_NEW 0x4b564d01
+#define MSR_KVM_ASYNC_PF_EN 0x4b564d02

#define KVM_MAX_MMU_OP_BATCH 32

+#define KVM_ASYNC_PF_ENABLED (1 << 0)
+
/* Operations for KVM_HC_MMU_OP */
#define KVM_MMU_OP_WRITE_PTE 1
#define KVM_MMU_OP_FLUSH_TLB 2
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index bf37397..68a3a06 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -788,12 +788,12 @@ EXPORT_SYMBOL_GPL(kvm_get_dr);
* kvm-specific. Those are put in the beginning of the list.
*/

-#define KVM_SAVE_MSRS_BEGIN 7
+#define KVM_SAVE_MSRS_BEGIN 8
static u32 msrs_to_save[] = {
MSR_KVM_SYSTEM_TIME, MSR_KVM_WALL_CLOCK,
MSR_KVM_SYSTEM_TIME_NEW, MSR_KVM_WALL_CLOCK_NEW,
HV_X64_MSR_GUEST_OS_ID, HV_X64_MSR_HYPERCALL,
- HV_X64_MSR_APIC_ASSIST_PAGE,
+ HV_X64_MSR_APIC_ASSIST_PAGE, MSR_KVM_ASYNC_PF_EN,
MSR_IA32_SYSENTER_CS, MSR_IA32_SYSENTER_ESP, MSR_IA32_SYSENTER_EIP,
MSR_STAR,
#ifdef CONFIG_X86_64
@@ -1431,6 +1431,29 @@ static int set_msr_hyperv(struct kvm_vcpu *vcpu, u32 msr, u64 data)
return 0;
}

+static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data)
+{
+ gpa_t gpa = data & ~0x3f;
+
+ /* Bits 1:5 are resrved, Should be zero */
+ if (data & 0x3e)
+ return 1;
+
+ vcpu->arch.apf.msr_val = data;
+
+ if (!(data & KVM_ASYNC_PF_ENABLED)) {
+ kvm_clear_async_pf_completion_queue(vcpu);
+ kvm_async_pf_hash_reset(vcpu);
+ return 0;
+ }
+
+ if (kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.apf.data, gpa))
+ return 1;
+
+ kvm_async_pf_wakeup_all(vcpu);
+ return 0;
+}
+
int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
{
switch (msr) {
@@ -1512,6 +1535,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
}
break;
}
+ case MSR_KVM_ASYNC_PF_EN:
+ if (kvm_pv_enable_async_pf(vcpu, data))
+ return 1;
+ break;
case MSR_IA32_MCG_CTL:
case MSR_IA32_MCG_STATUS:
case MSR_IA32_MC0_CTL ... MSR_IA32_MC0_CTL + 4 * KVM_MAX_MCE_BANKS - 1:
@@ -1788,6 +1815,9 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
case MSR_KVM_SYSTEM_TIME_NEW:
data = vcpu->arch.time;
break;
+ case MSR_KVM_ASYNC_PF_EN:
+ data = vcpu->arch.apf.msr_val;
+ break;
case MSR_IA32_P5_MC_ADDR:
case MSR_IA32_P5_MC_TYPE:
case MSR_IA32_MCG_CAP:
@@ -1935,6 +1965,7 @@ int kvm_dev_ioctl_check_extension(long ext)
case KVM_CAP_DEBUGREGS:
case KVM_CAP_X86_ROBUST_SINGLESTEP:
case KVM_CAP_XSAVE:
+ case KVM_CAP_ASYNC_PF:
r = 1;
break;
case KVM_CAP_COALESCED_MMIO:
@@ -5784,6 +5815,8 @@ free_vcpu:

void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
{
+ vcpu->arch.apf.msr_val = 0;
+
vcpu_load(vcpu);
kvm_mmu_unload(vcpu);
vcpu_put(vcpu);
@@ -5803,6 +5836,7 @@ int kvm_arch_vcpu_reset(struct kvm_vcpu *vcpu)
vcpu->arch.dr7 = DR7_FIXED_1;

kvm_make_request(KVM_REQ_EVENT, vcpu);
+ vcpu->arch.apf.msr_val = 0;

kvm_clear_async_pf_completion_queue(vcpu);
kvm_async_pf_hash_reset(vcpu);
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 919ae53..ea2dc1a 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -540,6 +540,7 @@ struct kvm_ppc_pvinfo {
#endif
#define KVM_CAP_PPC_GET_PVINFO 57
#define KVM_CAP_PPC_IRQ_LEVEL 58
+#define KVM_CAP_ASYNC_PF 59

#ifdef KVM_CAP_IRQ_ROUTING

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index dda88f2..5d09197 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -93,6 +93,7 @@ void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu);
void kvm_check_async_pf_completion(struct kvm_vcpu *vcpu);
int kvm_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, gfn_t gfn,
struct kvm_arch_async_pf *arch);
+int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
#endif

struct kvm_vcpu {
diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
index 41607ed..b276b06 100644
--- a/virt/kvm/async_pf.c
+++ b/virt/kvm/async_pf.c
@@ -190,3 +190,23 @@ retry_sync:
kmem_cache_free(async_pf_cache, work);
return 0;
}
+
+int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu)
+{
+ struct kvm_async_pf *work;
+
+ if (!list_empty(&vcpu->async_pf.done))
+ return 0;
+
+ work = kmem_cache_zalloc(async_pf_cache, GFP_ATOMIC);
+ if (!work)
+ return -ENOMEM;
+
+ work->page = bad_page;
+ get_page(bad_page);
+ INIT_LIST_HEAD(&work->queue); /* for list_del to work */
+
+ list_add_tail(&work->link, &vcpu->async_pf.done);
+ vcpu->async_pf.queued++;
+ return 0;