path: root/xen/arch/x86/i387.c

/*
 *  linux/arch/i386/kernel/i387.c
 *
 *  Copyright (C) 1994 Linus Torvalds
 *
 *  Pentium III FXSR, SSE support
 *  General FPU state handling cleanups
 *  Gareth Hughes <gareth@valinux.com>, May 2000
 */

#include <xen/config.h>
#include <xen/sched.h>
#include <asm/current.h>
#include <asm/processor.h>
#include <asm/hvm/support.h>
#include <asm/i387.h>
#include <asm/asm_defns.h>

static bool_t __read_mostly cpu_has_xsaveopt;

static void xsave(struct vcpu *v)
{
    struct xsave_struct *ptr = v->arch.xsave_area;

    asm volatile (
        ".byte " REX_PREFIX "0x0f,0xae,0x27"
        :
        : "a" (-1), "d" (-1), "D"(ptr)
        : "memory" );
}

static void xsaveopt(struct vcpu *v)
{
    struct xsave_struct *ptr = v->arch.xsave_area;

    asm volatile (
        ".byte " REX_PREFIX "0x0f,0xae,0x37"
        :
        : "a" (-1), "d" (-1), "D"(ptr)
        : "memory" );
}

static void xrstor(struct vcpu *v)
{
    struct xsave_struct *ptr = v->arch.xsave_area;

    /*
     * AMD CPUs don't save/restore FDP/FIP/FOP unless an exception
     * is pending. Clear the x87 state here by setting it to fixed
     * values. The hypervisor data segment can be sometimes 0 and
     * sometimes new user value. Both should be ok. Use the FPU saved
     * data block as a safe address because it should be in L1.
     */
    if ( (ptr->xsave_hdr.xstate_bv & XSTATE_FP) &&
         !(ptr->fpu_sse.fsw & 0x0080) &&
         boot_cpu_data.x86_vendor == X86_VENDOR_AMD )
        asm volatile ( "fnclex\n\t"        /* clear exceptions */
                       "ffree %%st(7)\n\t" /* clear stack tag */
                       "fildl %0"          /* load to clear state */
                       : : "m" (ptr->fpu_sse) );

    /*
     * XRSTOR can fault if passed a corrupted data block. We handle this
     * possibility, which may occur if the block was passed to us by control
     * tools or through VCPUOP_initialise, by silently clearing the block.
     */
    asm volatile ( "1: .byte " REX_PREFIX "0x0f,0xae,0x2f\n"
                   ".section .fixup,\"ax\"\n"
                   "2: mov %4,%%ecx       \n"
                   "   xor %1,%1          \n"
                   "   rep stosb          \n"
                   "   lea %3,%0          \n"
                   "   dec %1             \n"
                   "   jmp 1b             \n"
                   ".previous             \n"
                   _ASM_EXTABLE(1b, 2b)
                   : "+&D" (ptr)
                   : "a" (-1), "d" (-1), "m" (*ptr),
                     "m" (xsave_cntxt_size)
                   : "ecx" );
}

static void load_mxcsr(unsigned long val)
{
    val &= 0xffbf;
    asm volatile ( "ldmxcsr %0" : : "m" (val) );
}

static void init_fpu(void);
static void restore_fpu(struct vcpu *v);

void setup_fpu(struct vcpu *v)
{
    ASSERT(!is_idle_vcpu(v));

    /* Avoid recursion. */
    clts();

    if ( v->fpu_dirtied )
        return;

    if ( xsave_enabled(v) )
    {
        /*
         * XCR0 normally represents what guest OS set. In case of Xen itself, 
         * we set all supported feature mask before doing save/restore.
         */
        set_xcr0(v->arch.xcr0_accum);
        xrstor(v);
        set_xcr0(v->arch.xcr0);
    }
    else if ( v->fpu_initialised )
    {
        restore_fpu(v);
    }
    else
    {
        init_fpu();
    }

    v->fpu_initialised = 1;
    v->fpu_dirtied = 1;
}

static void init_fpu(void)
{
    asm volatile ( "fninit" );
    if ( cpu_has_xmm )
        load_mxcsr(0x1f80);
}

void save_init_fpu(struct vcpu *v)
{
    unsigned long cr0;
    char *fpu_ctxt;

    if ( !v->fpu_dirtied )
        return;

    ASSERT(!is_idle_vcpu(v));

    cr0 = read_cr0();
    fpu_ctxt = v->arch.guest_context.fpu_ctxt.x;

    /* This can happen, if a paravirtualised guest OS has set its CR0.TS. */
    if ( cr0 & X86_CR0_TS )
        clts();

    if ( xsave_enabled(v) )
    {
        /* XCR0 normally represents what guest OS set. In case of Xen itself,
         * we set all accumulated feature mask before doing save/restore.
         */
        set_xcr0(v->arch.xcr0_accum);
        if ( cpu_has_xsaveopt )
            xsaveopt(v);
        else
            xsave(v);
        set_xcr0(v->arch.xcr0);
    }
    else if ( cpu_has_fxsr )
    {
#ifdef __i386__
        asm volatile (
            "fxsave %0"
            : "=m" (*fpu_ctxt) );
#else /* __x86_64__ */
        /*
         * The only way to force fxsaveq on a wide range of gas versions. On 
         * older versions the rex64 prefix works only if we force an
         * addressing mode that doesn't require extended registers.
         */
        asm volatile (
            REX64_PREFIX "fxsave (%1)"
            : "=m" (*fpu_ctxt) : "cdaSDb" (fpu_ctxt) );
#endif

        /* Clear exception flags if FSW.ES is set. */
        if ( unlikely(fpu_ctxt[2] & 0x80) )
            asm volatile ("fnclex");

        /*
         * AMD CPUs don't save/restore FDP/FIP/FOP unless an exception
         * is pending. Clear the x87 state here by setting it to fixed
         * values. The hypervisor data segment can be sometimes 0 and
         * sometimes new user value. Both should be ok. Use the FPU saved
         * data block as a safe address because it should be in L1.
         */
        if ( boot_cpu_data.x86_vendor == X86_VENDOR_AMD )
        {
            asm volatile (
                "emms\n\t"  /* clear stack tags */
                "fildl %0"  /* load to clear state */
                : : "m" (*fpu_ctxt) );
        }
    }
    else
    {
        /* FWAIT is required to make FNSAVE synchronous. */
        asm volatile ( "fnsave %0 ; fwait" : "=m" (*fpu_ctxt) );
    }

    v->fpu_dirtied = 0;
    write_cr0(cr0|X86_CR0_TS);
}

static void restore_fpu(struct vcpu *v)
{
    char *fpu_ctxt = v->arch.guest_context.fpu_ctxt.x;

    /*
     * FXRSTOR can fault if passed a corrupted data block. We handle this
     * possibility, which may occur if the block was passed to us by control
     * tools or through VCPUOP_initialise, by silently clearing the block.
     */
    if ( cpu_has_fxsr )
    {
        asm volatile (
#ifdef __i386__
            "1: fxrstor %0            \n"
#else /* __x86_64__ */
            /* See above for why the operands/constraints are this way. */
            "1: " REX64_PREFIX "fxrstor (%2)\n"
#endif
            ".section .fixup,\"ax\"   \n"
            "2: push %%"__OP"ax       \n"
            "   push %%"__OP"cx       \n"
            "   push %%"__OP"di       \n"
            "   lea  %0,%%"__OP"di    \n"
            "   mov  %1,%%ecx         \n"
            "   xor  %%eax,%%eax      \n"
            "   rep ; stosl           \n"
            "   pop  %%"__OP"di       \n"
            "   pop  %%"__OP"cx       \n"
            "   pop  %%"__OP"ax       \n"
            "   jmp  1b               \n"
            ".previous                \n"
            _ASM_EXTABLE(1b, 2b)
            : 
            : "m" (*fpu_ctxt),
              "i" (sizeof(v->arch.guest_context.fpu_ctxt)/4)
#ifdef __x86_64__
             ,"cdaSDb" (fpu_ctxt)
#endif
            );
    }
    else
    {
        asm volatile ( "frstor %0" : : "m" (v->arch.guest_context.fpu_ctxt) );
    }
}

#define XSTATE_CPUID 0xd

/*
 * Maximum size (in byte) of the XSAVE/XRSTOR save area required by all
 * the supported and enabled features on the processor, including the
 * XSAVE.HEADER. We only enable XCNTXT_MASK that we have known.
 */
u32 xsave_cntxt_size;

/* A 64-bit bitmask of the XSAVE/XRSTOR features supported by processor. */
u64 xfeature_mask;

/* Cached xcr0 for fast read */
DEFINE_PER_CPU(uint64_t, xcr0);

void xsave_init(void)
{
    u32 eax, ebx, ecx, edx;
    int cpu = smp_processor_id();
    u32 min_size;

    if ( boot_cpu_data.cpuid_level < XSTATE_CPUID )
        return;

    cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);

    BUG_ON((eax & XSTATE_FP_SSE) != XSTATE_FP_SSE);
    BUG_ON((eax & XSTATE_YMM) && !(eax & XSTATE_SSE));

    /* FP/SSE, XSAVE.HEADER, YMM */
    min_size =  XSAVE_AREA_MIN_SIZE;
    if ( eax & XSTATE_YMM )
        min_size += XSTATE_YMM_SIZE;
    BUG_ON(ecx < min_size);

    /*
     * Set CR4_OSXSAVE and run "cpuid" to get xsave_cntxt_size.
     */
    set_in_cr4(X86_CR4_OSXSAVE);
    set_xcr0((((u64)edx << 32) | eax) & XCNTXT_MASK);
    cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);

    if ( cpu == 0 )
    {
        /*
         * xsave_cntxt_size is the max size required by enabled features.
         * We know FP/SSE and YMM about eax, and nothing about edx at present.
         */
        xsave_cntxt_size = ebx;
        xfeature_mask = eax + ((u64)edx << 32);
        xfeature_mask &= XCNTXT_MASK;
        printk("%s: using cntxt_size: 0x%x and states: 0x%"PRIx64"\n",
            __func__, xsave_cntxt_size, xfeature_mask);

        /* Check XSAVEOPT feature. */
        cpuid_count(XSTATE_CPUID, 1, &eax, &ebx, &ecx, &edx);
        cpu_has_xsaveopt = !!(eax & XSAVEOPT);
    }
    else
    {
        BUG_ON(xsave_cntxt_size != ebx);
        BUG_ON(xfeature_mask != (xfeature_mask & XCNTXT_MASK));
    }
}

int xsave_alloc_save_area(struct vcpu *v)
{
    struct xsave_struct *save_area;

    if ( !cpu_has_xsave || is_idle_vcpu(v) )
        return 0;

    BUG_ON(xsave_cntxt_size < XSAVE_AREA_MIN_SIZE);

    /* XSAVE/XRSTOR requires the save area be 64-byte-boundary aligned. */
    save_area = _xmalloc(xsave_cntxt_size, 64);
    if ( save_area == NULL )
        return -ENOMEM;

    memset(save_area, 0, xsave_cntxt_size);
    save_area->fpu_sse.fcw = FCW_DEFAULT;
    save_area->fpu_sse.mxcsr = MXCSR_DEFAULT;
    save_area->xsave_hdr.xstate_bv = XSTATE_FP_SSE;

    v->arch.xsave_area = save_area;
    v->arch.xcr0 = XSTATE_FP_SSE;
    v->arch.xcr0_accum = XSTATE_FP_SSE;

    return 0;
}

void xsave_free_save_area(struct vcpu *v)
{
    xfree(v->arch.xsave_area);
    v->arch.xsave_area = NULL;
}

bool_t xsave_enabled(const struct vcpu *v)
{
    if ( cpu_has_xsave )
    {
        ASSERT(xsave_cntxt_size >= XSAVE_AREA_MIN_SIZE);
        ASSERT(v->arch.xsave_area);
    }

    return cpu_has_xsave;	
}

/*
 * Local variables:
 * mode: C
 * c-set-style: "BSD"
 * c-basic-offset: 4
 * tab-width: 4
 * indent-tabs-mode: nil
 * End:
 */