KVM: MMU: hypercall based pte updates and TLB flushes

Hypercall based pte updates are faster than faults, and also allow use
of the lazy MMU mode to batch operations.

Don't report the feature if two dimensional paging is enabled.

[avi:
 - one mmu_op hypercall instead of one per op
 - allow 64-bit gpa on hypercall
 - don't pass host errors (-ENOMEM) to guest]

[akpm: warning fix on i386]

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 135 insertions, 1 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 414405b6ec13..072e9422c914 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -28,6 +28,7 @@
 #include <linux/module.h>
 #include <linux/swap.h>
 #include <linux/hugetlb.h>
+#include <linux/compiler.h>
 
 #include <asm/page.h>
 #include <asm/cmpxchg.h>
@@ -40,7 +41,7 @@
  * 2. while doing 1. it walks guest-physical to host-physical
  * If the hardware supports that we don't need to do shadow paging.
  */
-static bool tdp_enabled = false;
+bool tdp_enabled = false;
 
 #undef MMU_DEBUG
 
@@ -167,6 +168,13 @@ static int dbg = 1;
 #define ACC_USER_MASK    PT_USER_MASK
 #define ACC_ALL          (ACC_EXEC_MASK | ACC_WRITE_MASK | ACC_USER_MASK)
 
+struct kvm_pv_mmu_op_buffer {
+        void *ptr;
+        unsigned len;
+        unsigned processed;
+        char buf[512] __aligned(sizeof(long));
+};
+
 struct kvm_rmap_desc {
         u64 *shadow_ptes[RMAP_EXT];
         struct kvm_rmap_desc *more;
@@ -2003,6 +2011,132 @@ unsigned int kvm_mmu_calculate_mmu_pages(struct kvm *kvm)
         return nr_mmu_pages;
 }
 
+static void *pv_mmu_peek_buffer(struct kvm_pv_mmu_op_buffer *buffer,
+                                unsigned len)
+{
+        if (len > buffer->len)
+                return NULL;
+        return buffer->ptr;
+}
+
+static void *pv_mmu_read_buffer(struct kvm_pv_mmu_op_buffer *buffer,
+                                unsigned len)
+{
+        void *ret;
+
+        ret = pv_mmu_peek_buffer(buffer, len);
+        if (!ret)
+                return ret;
+        buffer->ptr += len;
+        buffer->len -= len;
+        buffer->processed += len;
+        return ret;
+}
+
+static int kvm_pv_mmu_write(struct kvm_vcpu *vcpu,
+                             gpa_t addr, gpa_t value)
+{
+        int bytes = 8;
+        int r;
+
+        if (!is_long_mode(vcpu) && !is_pae(vcpu))
+                bytes = 4;
+
+        r = mmu_topup_memory_caches(vcpu);
+        if (r)
+                return r;
+
+        if (!__emulator_write_phys(vcpu, addr, &value, bytes))
+                return -EFAULT;
+
+        return 1;
+}
+
+static int kvm_pv_mmu_flush_tlb(struct kvm_vcpu *vcpu)
+{
+        kvm_x86_ops->tlb_flush(vcpu);
+        return 1;
+}
+
+static int kvm_pv_mmu_release_pt(struct kvm_vcpu *vcpu, gpa_t addr)
+{
+        spin_lock(&vcpu->kvm->mmu_lock);
+        mmu_unshadow(vcpu->kvm, addr >> PAGE_SHIFT);
+        spin_unlock(&vcpu->kvm->mmu_lock);
+        return 1;
+}
+
+static int kvm_pv_mmu_op_one(struct kvm_vcpu *vcpu,
+                             struct kvm_pv_mmu_op_buffer *buffer)
+{
+        struct kvm_mmu_op_header *header;
+
+        header = pv_mmu_peek_buffer(buffer, sizeof *header);
+        if (!header)
+                return 0;
+        switch (header->op) {
+        case KVM_MMU_OP_WRITE_PTE: {
+                struct kvm_mmu_op_write_pte *wpte;
+
+                wpte = pv_mmu_read_buffer(buffer, sizeof *wpte);
+                if (!wpte)
+                        return 0;
+                return kvm_pv_mmu_write(vcpu, wpte->pte_phys,
+                                        wpte->pte_val);
+        }
+        case KVM_MMU_OP_FLUSH_TLB: {
+                struct kvm_mmu_op_flush_tlb *ftlb;
+
+                ftlb = pv_mmu_read_buffer(buffer, sizeof *ftlb);
+                if (!ftlb)
+                        return 0;
+                return kvm_pv_mmu_flush_tlb(vcpu);
+        }
+        case KVM_MMU_OP_RELEASE_PT: {
+                struct kvm_mmu_op_release_pt *rpt;
+
+                rpt = pv_mmu_read_buffer(buffer, sizeof *rpt);
+                if (!rpt)
+                        return 0;
+                return kvm_pv_mmu_release_pt(vcpu, rpt->pt_phys);
+        }
+        default: return 0;
+        }
+}
+
+int kvm_pv_mmu_op(struct kvm_vcpu *vcpu, unsigned long bytes,
+                  gpa_t addr, unsigned long *ret)
+{
+        int r;
+        struct kvm_pv_mmu_op_buffer buffer;
+
+        down_read(&vcpu->kvm->slots_lock);
+        down_read(&current->mm->mmap_sem);
+
+        buffer.ptr = buffer.buf;
+        buffer.len = min_t(unsigned long, bytes, sizeof buffer.buf);
+        buffer.processed = 0;
+
+        r = kvm_read_guest(vcpu->kvm, addr, buffer.buf, buffer.len);
+        if (r)
+                goto out;
+
+        while (buffer.len) {
+                r = kvm_pv_mmu_op_one(vcpu, &buffer);
+                if (r < 0)
+                        goto out;
+                if (r == 0)
+                        break;
+        }
+
+        r = 1;
+out:
+        *ret = buffer.processed;
+        up_read(&current->mm->mmap_sem);
+        up_read(&vcpu->kvm->slots_lock);
+        return r;
+}
+
 #ifdef AUDIT
 
 static const char *audit_msg;