On Mon, Jun 12, 2023 at 03:06:48AM +0000, Huang, Kai wrote: > 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(); If you want to play with barriers, assign pamt_4k_base the last with smp_store_release() and read it first in tdmr_get_pamt() with smp_load_acquire(). If it is non-zero, all pamt_* fields are valid. Or just drop this non-sense and use a spin lock for serialization. -- Kiryl Shutsemau / Kirill A. Shutemov
