Re: [Xen-devel] [PATCH 1/4] x86/svm: Clean up construct_vmcb()

[Jan Beulich <jbeulich@xxxxxxxx>]

On 04.12.2019 10:43, Andrew Cooper wrote:
> The vmcb is zeroed on allocate - drop all explicit writes of 0.  Move
> hvm_update_guest_efer() to co-locate it with the other control register
> updates.
> 
> Move the BUILD_BUG_ON() into build_assertions(), and add some offset checks
> for fields after the large blocks of reserved fields (as these are the most
> likely to trigger from a mis-edit).  Take the opportunity to fold 6 adjacent
> res* fields into one.
> 
> Finally, drop all trailing whitespace in the file.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
albeit with two (optional) suggestions:

> @@ -297,14 +258,26 @@ void __init setup_vmcb_dump(void)
>  
>  static void __init __maybe_unused build_assertions(void)
>  {
> -    struct segment_register sreg;
> +    struct vmcb_struct vmcb;
> +
> +    /* Build-time check of the VMCB layout. */
> +    BUILD_BUG_ON(sizeof(vmcb) != PAGE_SIZE);
> +    BUILD_BUG_ON(offsetof(struct vmcb_struct, _pause_filter_thresh) != 
> 0x03c);
> +    BUILD_BUG_ON(offsetof(struct vmcb_struct, _vintr)               != 
> 0x060);
> +    BUILD_BUG_ON(offsetof(struct vmcb_struct, eventinj)             != 
> 0x0a8);
> +    BUILD_BUG_ON(offsetof(struct vmcb_struct, es)                   != 
> 0x400);
> +    BUILD_BUG_ON(offsetof(struct vmcb_struct, _cpl)                 != 
> 0x4cb);
> +    BUILD_BUG_ON(offsetof(struct vmcb_struct, _cr4)                 != 
> 0x548);
> +    BUILD_BUG_ON(offsetof(struct vmcb_struct, rsp)                  != 
> 0x5d8);
> +    BUILD_BUG_ON(offsetof(struct vmcb_struct, rax)                  != 
> 0x5f8);
> +    BUILD_BUG_ON(offsetof(struct vmcb_struct, _g_pat)               != 
> 0x668);
>  
>      /* Check struct segment_register against the VMCB segment layout. */
> -    BUILD_BUG_ON(sizeof(sreg)       != 16);
> -    BUILD_BUG_ON(sizeof(sreg.sel)   != 2);
> -    BUILD_BUG_ON(sizeof(sreg.attr)  != 2);
> -    BUILD_BUG_ON(sizeof(sreg.limit) != 4);
> -    BUILD_BUG_ON(sizeof(sreg.base)  != 8);
> +    BUILD_BUG_ON(sizeof(vmcb.es)       != 16);
> +    BUILD_BUG_ON(sizeof(vmcb.es.sel)   != 2);
> +    BUILD_BUG_ON(sizeof(vmcb.es.attr)  != 2);
> +    BUILD_BUG_ON(sizeof(vmcb.es.limit) != 4);
> +    BUILD_BUG_ON(sizeof(vmcb.es.base)  != 8);
>      BUILD_BUG_ON(offsetof(struct segment_register, sel)   != 0);
>      BUILD_BUG_ON(offsetof(struct segment_register, attr)  != 2);
>      BUILD_BUG_ON(offsetof(struct segment_register, limit) != 4);

For the ones only supplying context here, how about using the
shorter offsetof(typeof(vmcb.es), ...), also tying things better
to the prior sizeof() checks? The same, albeit to a lesser degree,
might then go for the earlier block, which could use the shorter
typeof(vmcb).

> --- a/xen/include/asm-x86/hvm/svm/vmcb.h
> +++ b/xen/include/asm-x86/hvm/svm/vmcb.h
> @@ -406,12 +406,7 @@ struct vmcb_struct {
>      u32 _exception_intercepts;  /* offset 0x08 - cleanbit 0 */
>      u32 _general1_intercepts;   /* offset 0x0C - cleanbit 0 */
>      u32 _general2_intercepts;   /* offset 0x10 - cleanbit 0 */
> -    u32 res01;                  /* offset 0x14 */
> -    u64 res02;                  /* offset 0x18 */
> -    u64 res03;                  /* offset 0x20 */
> -    u64 res04;                  /* offset 0x28 */
> -    u64 res05;                  /* offset 0x30 */
> -    u32 res06;                  /* offset 0x38 */
> +    u32 res01[10];

Was it intentional for the comment to be lost altogether?

Jan

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