Hi Deepak On Thu, Nov 14, 2024 at 11:50 PM Deepak Gupta <debug@xxxxxxxxxxxx> wrote: > > > Hi Nick, > > Thanks for reviewing and helping. > > On Thu, Nov 14, 2024 at 02:17:30PM +0800, Nick Hu wrote: > >Hi Deepak > > > >On Thu, Nov 14, 2024 at 9:25 AM Deepak Gupta <debug@xxxxxxxxxxxx> wrote: > >> > >> On Thu, Nov 14, 2024 at 09:20:14AM +0800, Nick Hu wrote: > >> >Hi Deepak > >> > > >> >On Thu, Nov 14, 2024 at 9:06 AM Deepak Gupta <debug@xxxxxxxxxxxx> wrote: > >> >> >> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S > >> >> >> index 356d5397b2a2..6244408ca917 100644 > >> >> >> --- a/arch/riscv/kernel/head.S > >> >> >> +++ b/arch/riscv/kernel/head.S > >> >> >> @@ -164,6 +164,12 @@ secondary_start_sbi: > >> >> >> call relocate_enable_mmu > >> >> >> #endif > >> >> >> call .Lsetup_trap_vector > >> >> >> + li a7, SBI_EXT_FWFT > >> >> >> + li a6, SBI_EXT_FWFT_SET > >> >> >> + li a0, SBI_FWFT_SHADOW_STACK > >> >> >> + li a1, 1 /* enable supervisor to access shadow stack access */ > >> >> >> + li a2, SBI_FWFT_SET_FLAG_LOCK > >> >> >> + ecall > >> >> >> scs_load_current > >> >> >> call smp_callin > >> >> >> #endif /* CONFIG_SMP */ > >> >> >> @@ -320,6 +326,12 @@ SYM_CODE_START(_start_kernel) > >> >> >> la tp, init_task > >> >> >> la sp, init_thread_union + THREAD_SIZE > >> >> >> addi sp, sp, -PT_SIZE_ON_STACK > >> >> >> + li a7, SBI_EXT_FWFT > >> >> >> + li a6, SBI_EXT_FWFT_SET > >> >> >> + li a0, SBI_FWFT_SHADOW_STACK > >> >> >> + li a1, 1 /* enable supervisor to access shadow stack access */ > >> >> >> + li a2, SBI_FWFT_SET_FLAG_LOCK > >> >> >> + ecall > >> >> >> scs_load_current > >> >> >> > >> >> >> #ifdef CONFIG_KASAN > >> >> >> > >> >> >> -- > >> >> >> 2.45.0 > >> >> >> > >> >> >Should we clear the SBI_FWFT_SET_FLAG_LOCK before the cpu hotplug > >> >> >otherwise the menvcfg.sse won't be set by the fwft set sbi call when > >> >> >the hotplug cpu back to kernel? > >> >> > >> >> Hmm... > >> >> > >> >> An incoming hotplug CPU has no features setup on it. > >> >> I see that `sbi_cpu_start` will supply `secondary_start_sbi` as start > >> >> up code for incoming CPU. `secondary_start_sbi` is in head.S which converges > >> >> in `.Lsecondary_start_common`. And thus hotplugged CPU should be > >> >> issuing shadow stack set FWFT sbi as well. > >> >> > >> >> Am I missing something ? > >> >> > >> >This is the correct flow. However the opensbi will deny it due to the > >> >SBI_FWFT_SET_FLAG_LOCK already being set. > >> >So the menvcfg.sse will not set by this flow. > >> > > >> >if (conf->flags & SBI_FWFT_SET_FLAG_LOCK) > >> > return SBI_EDENIED; > >> > > >> > >> hmm... Why? > >> > >> `conf` is pointing to per-hart state in firmware. > >> > >> On this incoming cpu, opensbi (or equivalent) firmware must have > >> ensured that this per-hart state doesn't have lock set. > >> > >> Am I missing something? > >> > >Current OpenSBI doesn't clear the lock in the warm init of the hotplug path. > >It seems like we need a patch to address it. > > Got it thanks. > Since you already know what's the problem, can you send a patch to opensbi. > If you want rather have me do it, let me know. Thanks. > No problem. I'll send a patch to opensbi. Regards, Nick > > > >Regards, > >Nick > >> >Regards, > >> >Nick > >> >> > > >> >> >Regards, > >> >> >Nick > >> >> >> > >> >> >> _______________________________________________ > >> >> >> linux-riscv mailing list > >> >> >> linux-riscv@xxxxxxxxxxxxxxxxxxx > >> >> >> http://lists.infradead.org/mailman/listinfo/linux-riscv
