[PATCH 038/104] KVM: Use alignment properties of vcpu to simplify FPU ops

Avi Kivity
2007-09-17T08:40:21Z

From: Rusty Russell <rusty@rustcorp.com.au>

Now we use a kmem cache for allocating vcpus, we can get the 16-byte
alignment required by fxsave & fxrstor instructions, and avoid
manually aligning the buffer.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Avi Kivity <avi@qumranet.com>
---
drivers/kvm/kvm.h | 13 ++++---------
drivers/kvm/kvm_main.c | 45 +++++++++++++++++----------------------------
drivers/kvm/svm.c | 8 ++++----
3 files changed, 25 insertions(+), 41 deletions(-)

diff --git a/drivers/kvm/kvm.h b/drivers/kvm/kvm.h
index b362e8f..7a34706 100644
--- a/drivers/kvm/kvm.h
+++ b/drivers/kvm/kvm.h
@@ -45,10 +45,6 @@
#define KVM_REFILL_PAGES 25
#define KVM_MAX_CPUID_ENTRIES 40

-#define FX_IMAGE_SIZE 512
-#define FX_IMAGE_ALIGN 16
-#define FX_BUF_SIZE (2 * FX_IMAGE_SIZE + FX_IMAGE_ALIGN)
-
#define DE_VECTOR 0
#define NM_VECTOR 7
#define DF_VECTOR 8
@@ -342,9 +338,8 @@ struct kvm_vcpu {

struct kvm_guest_debug guest_debug;

- char fx_buf[FX_BUF_SIZE];
- char *host_fx_image;
- char *guest_fx_image;
+ struct i387_fxsave_struct host_fx_image;
+ struct i387_fxsave_struct guest_fx_image;
int fpu_active;
int guest_fpu_loaded;

@@ -704,12 +699,12 @@ static inline unsigned long read_msr(unsigned long msr)
}
#endif

-static inline void fx_save(void *image)
+static inline void fx_save(struct i387_fxsave_struct *image)
{
asm ("fxsave (%0)":: "r" (image));
}

-static inline void fx_restore(void *image)
+static inline void fx_restore(struct i387_fxsave_struct *image)
{
asm ("fxrstor (%0)":: "r" (image));
}
diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index 4166a08..bfb1b6d 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -154,8 +154,8 @@ void kvm_load_guest_fpu(struct kvm_vcpu *vcpu)
return;

vcpu->guest_fpu_loaded = 1;
- fx_save(vcpu->host_fx_image);
- fx_restore(vcpu->guest_fx_image);
+ fx_save(&vcpu->host_fx_image);
+ fx_restore(&vcpu->guest_fx_image);
}
EXPORT_SYMBOL_GPL(kvm_load_guest_fpu);

@@ -165,8 +165,8 @@ void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
return;

vcpu->guest_fpu_loaded = 0;
- fx_save(vcpu->guest_fx_image);
- fx_restore(vcpu->host_fx_image);
+ fx_save(&vcpu->guest_fx_image);
+ fx_restore(&vcpu->host_fx_image);
}
EXPORT_SYMBOL_GPL(kvm_put_guest_fpu);

@@ -262,10 +262,6 @@ int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id)
}
vcpu->pio_data = page_address(page);

- vcpu->host_fx_image = (char*)ALIGN((hva_t)vcpu->fx_buf,
- FX_IMAGE_ALIGN);
- vcpu->guest_fx_image = vcpu->host_fx_image + FX_IMAGE_SIZE;
-
r = kvm_mmu_create(vcpu);
if (r < 0)
goto fail_free_pio_data;
@@ -615,30 +611,20 @@ EXPORT_SYMBOL_GPL(set_cr8);

void fx_init(struct kvm_vcpu *vcpu)
{
- struct __attribute__ ((__packed__)) fx_image_s {
- u16 control; //fcw
- u16 status; //fsw
- u16 tag; // ftw
- u16 opcode; //fop
- u64 ip; // fpu ip
- u64 operand;// fpu dp
- u32 mxcsr;
- u32 mxcsr_mask;
-
- } *fx_image;
+ unsigned after_mxcsr_mask;

/* Initialize guest FPU by resetting ours and saving into guest's */
preempt_disable();
- fx_save(vcpu->host_fx_image);
+ fx_save(&vcpu->host_fx_image);
fpu_init();
- fx_save(vcpu->guest_fx_image);
- fx_restore(vcpu->host_fx_image);
+ fx_save(&vcpu->guest_fx_image);
+ fx_restore(&vcpu->host_fx_image);
preempt_enable();

- fx_image = (struct fx_image_s *)vcpu->guest_fx_image;
- fx_image->mxcsr = 0x1f80;
- memset(vcpu->guest_fx_image + sizeof(struct fx_image_s),
- 0, FX_IMAGE_SIZE - sizeof(struct fx_image_s));
+ after_mxcsr_mask = offsetof(struct i387_fxsave_struct, st_space);
+ vcpu->guest_fx_image.mxcsr = 0x1f80;
+ memset((void *)&vcpu->guest_fx_image + after_mxcsr_mask,
+ 0, sizeof(struct i387_fxsave_struct) - after_mxcsr_mask);
}
EXPORT_SYMBOL_GPL(fx_init);

@@ -2356,6 +2342,9 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, int n)

preempt_notifier_init(&vcpu->preempt_notifier, &kvm_preempt_ops);

+ /* We do fxsave: this must be aligned. */
+ BUG_ON((unsigned long)&vcpu->host_fx_image & 0xF);
+
vcpu_load(vcpu);
r = kvm_mmu_setup(vcpu);
vcpu_put(vcpu);
@@ -2468,7 +2457,7 @@ struct fxsave {

static int kvm_vcpu_ioctl_get_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)
{
- struct fxsave *fxsave = (struct fxsave *)vcpu->guest_fx_image;
+ struct fxsave *fxsave = (struct fxsave *)&vcpu->guest_fx_image;

vcpu_load(vcpu);

@@ -2488,7 +2477,7 @@ static int kvm_vcpu_ioctl_get_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)

static int kvm_vcpu_ioctl_set_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)
{
- struct fxsave *fxsave = (struct fxsave *)vcpu->guest_fx_image;
+ struct fxsave *fxsave = (struct fxsave *)&vcpu->guest_fx_image;

vcpu_load(vcpu);

diff --git a/drivers/kvm/svm.c b/drivers/kvm/svm.c
index 8193651..5277084 100644
--- a/drivers/kvm/svm.c
+++ b/drivers/kvm/svm.c
@@ -1557,8 +1557,8 @@ again:
}

if (vcpu->fpu_active) {
- fx_save(vcpu->host_fx_image);
- fx_restore(vcpu->guest_fx_image);
+ fx_save(&vcpu->host_fx_image);
+ fx_restore(&vcpu->guest_fx_image);
}

asm volatile (
@@ -1670,8 +1670,8 @@ again:
vcpu->guest_mode = 0;

if (vcpu->fpu_active) {
- fx_save(vcpu->guest_fx_image);
- fx_restore(vcpu->host_fx_image);
+ fx_save(&vcpu->guest_fx_image);
+ fx_restore(&vcpu->host_fx_image);
}

if ((svm->vmcb->save.dr7 & 0xff))
--
1.5.3