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KVM: Use alignment properties of vcpu to simplify FPU ops
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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>
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Rusty Russell authored and Avi Kivity committed Oct 13, 2007
1 parent c16f862 commit b114b08
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Showing 3 changed files with 25 additions and 41 deletions.
13 changes: 4 additions & 9 deletions drivers/kvm/kvm.h
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Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down Expand Up @@ -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;

Expand Down Expand Up @@ -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));
}
Expand Down
45 changes: 17 additions & 28 deletions drivers/kvm/kvm_main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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);

Expand All @@ -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);

Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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);

Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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);

Expand All @@ -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);

Expand Down
8 changes: 4 additions & 4 deletions drivers/kvm/svm.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1557,8 +1557,8 @@ static int svm_vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
}

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 (
Expand Down Expand Up @@ -1670,8 +1670,8 @@ static int svm_vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
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))
Expand Down

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