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@rivosinc.com 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@rivosinc.com 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_FWFTli a6, SBI_EXT_FWFT_SETli a0, SBI_FWFT_SHADOW_STACKli a1, 1 /* enable supervisor to access shadow stack access */li a2, SBI_FWFT_SET_FLAG_LOCKecall 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_FWFTli a6, SBI_EXT_FWFT_SETli a0, SBI_FWFT_SHADOW_STACKli a1, 1 /* enable supervisor to access shadow stack access */li a2, SBI_FWFT_SET_FLAG_LOCKecall 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.
Regards, Nick
Regards, Nick
Regards, Nick
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