Re: [PATCH] x86: Implement Linear Address Masking support

[Richard Henderson]

On 4/6/22 20:01, Kirill A. Shutemov wrote:
> Linear Address Masking feature makes CPU ignore some bits of the virtual
> address. These bits can be used to encode metadata.
>
> The feature is enumerated with CPUID.(EAX=07H, ECX=01H):EAX.LAM[bit 26].
>
> CR3.LAM_U57[bit 62] allows to encode 6 bits of metadata in bits 62:57 of
> user pointers.
>
> CR3.LAM_U48[bit 61] allows to encode 15 bits of metadata in bits 62:48
> of user pointers.
>
> CR4.LAM_SUP[bit 28] allows to encode metadata of supervisor pointers.
> If 5-level paging is in use, 6 bits of metadata can be encoded in 62:57.
> For 4-level paging, 15 bits of metadata can be encoded in bits 62:48.
>
> QEMU strips address from the metadata bits and gets it to canonical
> shape before handling memory access. It has to be done very early before
> TLB lookup.

The new hook is incorrect, in that it doesn't apply to addresses along the tlb 
fast path.

But it isn't really needed.  You can do all of the work in the existing tlb_fill hook. 
AArch64 has a similar feature, and that works fine.


r~