Re: [PATCHv9 08/17] x86/tdx: Account shared memory

[Kuppuswamy Sathyanarayanan]

On 3/25/24 3:39 AM, Kirill A. Shutemov wrote:
> The kernel will convert all shared memory back to private during kexec.
> The direct mapping page tables will provide information on which memory
> is shared.
>
> It is extremely important to convert all shared memory. If a page is
> missed, it will cause the second kernel to crash when it accesses it.
>
> Keep track of the number of shared pages. This will allow for
> cross-checking against the shared information in the direct mapping and
> reporting if the shared bit is lost.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> ---

Looks good to me.

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>

>  arch/x86/coco/tdx/tdx.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
> index 26fa47db5782..979891e97d83 100644
> --- a/arch/x86/coco/tdx/tdx.c
> +++ b/arch/x86/coco/tdx/tdx.c
> @@ -38,6 +38,8 @@
>  
>  #define TDREPORT_SUBTYPE_0	0
>  
> +static atomic_long_t nr_shared;
> +
>  /* Called from __tdx_hypercall() for unrecoverable failure */
>  noinstr void __noreturn __tdx_hypercall_failed(void)
>  {
> @@ -821,6 +823,11 @@ static int tdx_enc_status_change_finish(unsigned long vaddr, int numpages,
>  	if (!enc && !tdx_enc_status_changed(vaddr, numpages, enc))
>  		return -EIO;
>  
> +	if (enc)
> +		atomic_long_sub(numpages, &nr_shared);
> +	else
> +		atomic_long_add(numpages, &nr_shared);
> +
>  	return 0;
>  }
>  

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer