Re: [Xen-devel] [PATCH] x86/xsave: provide guests with finit-like environment

[Keir Fraser <keir@xxxxxxx>]

On 17/11/2011 14:43, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:

> Without the use of xsave, guests get their initial floating point
> environment set up with finit. At least NetWare actually depends on
> this (in particular on all exceptions being masked), so to be
> consistent set the same environment also when using xsave. This is
> also in line with all SSE exceptions getting masked initially.
> 
> To avoid further fragile casts in xstate_alloc_save_area() the patch
> also changes xsave_struct's fpu_see member to have actually usable
> fields.
> 
> The patch was tested in its technically identical, but modified-file-
> wise different 4.1.2 version.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> Tested-by: Charles Arnold <carnold@xxxxxxxx>

Acked-by: Keir Fraser <keir@xxxxxxx>

> --- a/xen/arch/x86/i387.c
> +++ b/xen/arch/x86/i387.c
> @@ -17,7 +17,6 @@
>  #include <asm/xstate.h>
>  #include <asm/asm_defns.h>
>  
> -#define MXCSR_DEFAULT 0x1f80
>  static void fpu_init(void)
>  {
>      unsigned long val;
> --- a/xen/arch/x86/xstate.c
> +++ b/xen/arch/x86/xstate.c
> @@ -97,7 +97,7 @@ bool_t xsave_enabled(const struct vcpu *
>  
>  int xstate_alloc_save_area(struct vcpu *v)
>  {
> -    void *save_area;
> +    struct xsave_struct *save_area;
>  
>      if ( !cpu_has_xsave || is_idle_vcpu(v) )
>          return 0;
> @@ -109,8 +109,9 @@ int xstate_alloc_save_area(struct vcpu *
>      if ( save_area == NULL )
>          return -ENOMEM;
>  
> -    ((u32 *)save_area)[6] = 0x1f80;  /* MXCSR */
> -    *(uint64_t *)(save_area + 512) = XSTATE_FP_SSE;  /* XSETBV */
> +    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;
> --- a/xen/include/asm-x86/xstate.h
> +++ b/xen/include/asm-x86/xstate.h
> @@ -11,6 +11,9 @@
>  #include <xen/types.h>
>  #include <xen/percpu.h>
>  
> +#define FCW_DEFAULT               0x037f
> +#define MXCSR_DEFAULT             0x1f80
> +
>  #define XSTATE_CPUID              0x0000000d
>  #define XSTATE_FEATURE_XSAVEOPT   (1 << 0)    /* sub-leaf 1, eax[bit 0] */
>  
> @@ -46,7 +49,29 @@ extern u64 xfeature_mask;
>  /* extended state save area */
>  struct xsave_struct
>  {
> -    struct { char x[512]; } fpu_sse;         /* FPU/MMX, SSE */
> +    union {                                  /* FPU/MMX, SSE */
> +        char x[512];
> +        struct {
> +            uint16_t fcw;
> +            uint16_t fsw;
> +            uint8_t ftw;
> +            uint8_t rsvd1;
> +            uint16_t fop;
> +            union {
> +#ifdef __x86_64__
> +                uint64_t addr;
> +#endif
> +                struct {
> +                    uint32_t offs;
> +                    uint16_t sel;
> +                    uint16_t rsvd;
> +                };
> +            } fip, fdp;
> +            uint32_t mxcsr;
> +            uint32_t mxcsr_mask;
> +            /* data registers follow here */
> +        };
> +    } fpu_sse;
>  
>      struct {
>          u64 xstate_bv;
> 
> 
> 
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