On Fri, 2023-06-09 at 16:23 +0300, kirill.shutemov@xxxxxxxxxxxxxxx wrote:
> 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?
Hmm.. Right. Sorry I missed.
>
> 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];
>
I think a simple memory barrier will do. How does below look?
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -591,11 +591,12 @@ static int tdmr_set_up_pamt(struct tdmr_info *tdmr,
* 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.
+ * is firstly set and place a __mb() after it otherwise
+ * tdx_memory_shutdown() may get an invalid PAMT base
+ * when it sees a valid number of PAMT pages.
*/
tdmr->pamt_4k_base = pamt_base[TDX_PS_4K];
+ __mb();
