Re: [PATCH v11 18/20] x86: Handle TDX erratum to reset TDX private memory during kexec() and reboot

From: kirill . shutemov
Date: Fri Jun 09 2023 - 09:23:14 EST


On Mon, Jun 05, 2023 at 02:27:31AM +1200, Kai Huang wrote:
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index 8ff07256a515..0aa413b712e8 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -587,6 +587,14 @@ static int tdmr_set_up_pamt(struct tdmr_info *tdmr,
> tdmr_pamt_base += pamt_size[pgsz];
> }
>
> + /*
> + * tdx_memory_shutdown() also reads TDMR's PAMT during
> + * kexec() or reboot, which could happen at anytime, even
> + * during this particular code. Make sure pamt_4k_base
> + * is firstly set otherwise tdx_memory_shutdown() may
> + * get an invalid PAMT base when it sees a valid number
> + * of PAMT pages.
> + */

Hmm? What prevents compiler from messing this up. It can reorder as it
wishes, no?

Maybe add a proper locking? Anything that prevent preemption would do,
right?

> tdmr->pamt_4k_base = pamt_base[TDX_PS_4K];
> tdmr->pamt_4k_size = pamt_size[TDX_PS_4K];
> tdmr->pamt_2m_base = pamt_base[TDX_PS_2M];

--
Kiryl Shutsemau / Kirill A. Shutemov