Re: [Xen-devel] [PATCH V3 5/6] x86/xsaves: support compact format for hvm save/restore

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 05/08/15 02:57, Shuai Ruan wrote:
> xsaves/xrstors only use compact format, so format convertion
> is needed when perform save/restore.
>
> Signed-off-by: Shuai Ruan <shuai.ruan@xxxxxxxxxxxxxxx>
> ---
>  xen/arch/x86/domain.c        |   3 +
>  xen/arch/x86/hvm/hvm.c       |  16 +++--
>  xen/arch/x86/xstate.c        | 138 
> +++++++++++++++++++++++++++++++++++++++++++
>  xen/include/asm-x86/xstate.h |   6 ++
>  4 files changed, 158 insertions(+), 5 deletions(-)
>
> diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
> index e8b8d67..083b70d 100644
> --- a/xen/arch/x86/domain.c
> +++ b/xen/arch/x86/domain.c
> @@ -845,6 +845,9 @@ int arch_set_info_guest(
>          memcpy(v->arch.fpu_ctxt, &c.nat->fpu_ctxt, sizeof(c.nat->fpu_ctxt));
>          if ( v->arch.xsave_area )
>               v->arch.xsave_area->xsave_hdr.xstate_bv = XSTATE_FP_SSE;
> +        if ( cpu_has_xsaves )
> +            v->arch.xsave_area->xsave_hdr.xcomp_bv = v->arch.xcr0_accum |
> +                                                     
> XSTATE_COMPACTION_ENABLED;
>      }
>  
>      if ( !compat )
> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
> index e5cf761..8495938 100644
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -2127,8 +2127,11 @@ static int hvm_save_cpu_xsave_states(struct domain *d, 
> hvm_domain_context_t *h)
>          ctxt->xfeature_mask = xfeature_mask;
>          ctxt->xcr0 = v->arch.xcr0;
>          ctxt->xcr0_accum = v->arch.xcr0_accum;
> -        memcpy(&ctxt->save_area, v->arch.xsave_area,
> -               size - offsetof(struct hvm_hw_cpu_xsave, save_area));
> +        if ( cpu_has_xsaves )
> +            save_xsave_states(v, (u8 *)&ctxt->save_area);

This absolutely needs to take a size parameter, and looks like it should
take a void pointer.

> +        else
> +            memcpy(&ctxt->save_area, v->arch.xsave_area,
> +                   size - offsetof(struct hvm_hw_cpu_xsave, save_area));
>      }
>  
>      return 0;
> @@ -2227,9 +2230,12 @@ static int hvm_load_cpu_xsave_states(struct domain *d, 
> hvm_domain_context_t *h)
>      v->arch.xcr0_accum = ctxt->xcr0_accum;
>      if ( ctxt->xcr0_accum & XSTATE_NONLAZY )
>          v->arch.nonlazy_xstate_used = 1;
> -    memcpy(v->arch.xsave_area, &ctxt->save_area,
> -           min(desc->length, size) - offsetof(struct hvm_hw_cpu_xsave,
> -           save_area));
> +    if ( cpu_has_xsaves )
> +        load_xsave_states(v, (u8 *)&ctxt->save_area);
> +    else
> +        memcpy(v->arch.xsave_area, &ctxt->save_area,
> +               min(desc->length, size) - offsetof(struct hvm_hw_cpu_xsave,
> +               save_area));
>  
>      return 0;
>  }
> diff --git a/xen/arch/x86/xstate.c b/xen/arch/x86/xstate.c
> index 699058d..0eea146 100644
> --- a/xen/arch/x86/xstate.c
> +++ b/xen/arch/x86/xstate.c
> @@ -29,6 +29,9 @@ static u32 __read_mostly xsave_cntxt_size;
>  /* A 64-bit bitmask of the XSAVE/XRSTOR features supported by processor. */
>  u64 __read_mostly xfeature_mask;
>  
> +static unsigned int *xstate_offsets, *xstate_sizes;
> +static unsigned int xstate_features;
> +static unsigned int xstate_comp_offsets[sizeof(xfeature_mask)*8];
>  /* Cached xcr0 for fast read */
>  static DEFINE_PER_CPU(uint64_t, xcr0);
>  
> @@ -65,6 +68,135 @@ uint64_t get_xcr0(void)
>      return this_cpu(xcr0);
>  }
>  
> +static void setup_xstate_features(void)
> +{
> +    unsigned int eax, ebx, ecx, edx, leaf = 0x2;
> +
> +    xstate_features = fls(xfeature_mask);
> +    xstate_offsets = _xzalloc(xstate_features, sizeof(int));
> +    xstate_sizes = _xzalloc(xstate_features, sizeof(int));

Don't mix and match types.  xzalloc_array() is what you should use.

> +
> +    do {
> +        cpuid_count(XSTATE_CPUID, leaf, &eax, &ebx, &ecx, &edx);
> +
> +        if ( eax == 0 )
> +            break;
> +
> +        xstate_offsets[leaf] = ebx;
> +        xstate_sizes[leaf] = eax;
> +
> +        leaf++;
> +    } while (1);

This is erroneous if there is a break in the feature bits, and liable to
wander off the end of the array.

This loop should be a for loop over set bits in xfeature_mask, not an
infinite while loop.

> +}
> +
> +static void setup_xstate_comp(void)
> +{
> +    unsigned int xstate_comp_sizes[sizeof(xfeature_mask)*8];
> +    int i;

unsigned int.

> +
> +    /*
> +     * The FP xstates and SSE xstates are legacy states. They are always
> +     * in the fixed offsets in the xsave area in either compacted form
> +     * or standard form.
> +     */
> +    xstate_comp_offsets[0] = 0;
> +    xstate_comp_offsets[1] = XSAVE_SSE_OFFSET;
> +
> +    xstate_comp_offsets[2] = FXSAVE_SIZE + XSAVE_HDR_SIZE;
> +
> +    for (i = 2; i < xstate_features; i++)

This loop will run off the end of xstate_comp_sizes[] for any processor
supporting AVX512 or greater.

> +    {
> +        if ( 1 << i & xfeature_mask )
You definitely need some brackets here.

> +            xstate_comp_sizes[i] = xstate_sizes[i];
> +        else
> +            xstate_comp_sizes[i] = 0;
> +
> +        if ( i > 2 )
> +            xstate_comp_offsets[i] = xstate_comp_offsets[i-1]
> +                                    + xstate_comp_sizes[i-1];
> +    }
> +}
> +
> +static void *get_xsave_addr(struct xsave_struct *xsave, int xstate)
> +{
> +    int feature = fls(xstate) - 1;
> +    if ( !(1 << feature & xfeature_mask) )
> +        return NULL;
> +
> +    return (void *)xsave + xstate_comp_offsets[feature];
> +}
> +
> +void save_xsave_states(struct vcpu *v, u8 *dest)
> +{
> +    struct xsave_struct *xsave = v->arch.xsave_area;
> +    u64 xstate_bv = xsave->xsave_hdr.xstate_bv;
> +    u64 valid;
> +
> +    /*
> +     * Copy legacy XSAVE area, to avoid complications with CPUID
> +     * leaves 0 and 1 in the loop below.
> +     */
> +    memcpy(dest, xsave, XSAVE_HDR_OFFSET);
> +
> +    /* Set XSTATE_BV */
> +    *(u64 *)(dest + XSAVE_HDR_OFFSET) = xstate_bv;
> +
> +    /*
> +     * Copy each region from the possibly compacted offset to the
> +     * non-compacted offset.
> +     */
> +    valid = xstate_bv & ~XSTATE_FP_SSE;
> +    while ( valid )
> +    {
> +        u64 feature = valid & -valid;
> +        int index = fls(feature) - 1;
> +        void *src = get_xsave_addr(xsave, feature);
> +
> +        if ( src )
> +            memcpy(dest + xstate_offsets[index], src, xstate_sizes[index]);
> +        else
> +            WARN_ON(1);

These WARN_ON()s are of no use whatsoever.  They should either be
dropped, or turned to BUG() after printing some emergency state.

> +
> +        valid -= feature;
> +    }
> +}
> +
> +void load_xsave_states(struct vcpu *v, u8 *src)
> +{
> +    struct xsave_struct *xsave = v->arch.xsave_area;
> +    u64 xstate_bv = *(u64 *)(src + XSAVE_HDR_OFFSET);
> +    u64 valid;
> +
> +    /*
> +     * Copy legacy XSAVE area, to avoid complications with CPUID
> +     * leaves 0 and 1 in the loop below.
> +     */
> +    memcpy(xsave, src, XSAVE_HDR_OFFSET);
> +
> +    /* Set XSTATE_BV and possibly XCOMP_BV.  */
> +    xsave->xsave_hdr.xstate_bv = xstate_bv;
> +    xsave->xsave_hdr.xcomp_bv = v->arch.xcr0_accum | 
> XSTATE_COMPACTION_ENABLED;
> +
> +    /*
> +     * Copy each region from the non-compacted offset to the
> +     * possibly compacted offset.
> +     */
> +    valid = xstate_bv & ~XSTATE_FP_SSE;
> +    while ( valid )
> +    {
> +        u64 feature = valid & -valid;
> +        int index = fls(feature) - 1;
> +        void *dest = get_xsave_addr(xsave, feature);
> +
> +        if (dest)
> +            memcpy(dest, src + xstate_offsets[index], xstate_sizes[index]);
> +     else
> +            WARN_ON(1);

Tabs.

~Andrew

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