Messages in this thread | | | From | Lai Jiangshan <> | Date | Fri, 17 Mar 2023 21:35:57 +0800 | Subject | Re: [PATCH v5 22/34] x86/fred: FRED initialization code |
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Hello
Comments in cpu_init_fred_exceptions() seem scarce for understanding.
On Tue, Mar 7, 2023 at 11:07 AM Xin Li <xin3.li@intel.com> wrote:
> +/* > + * Initialize FRED on this CPU. This cannot be __init as it is called > + * during CPU hotplug. > + */ > +void cpu_init_fred_exceptions(void) > +{ > + wrmsrl(MSR_IA32_FRED_CONFIG, > + FRED_CONFIG_ENTRYPOINT(fred_entrypoint_user) | > + FRED_CONFIG_REDZONE(8) | /* Reserve for CALL emulation */ > + FRED_CONFIG_INT_STKLVL(0));
What is it about "Reserve for CALL emulation"?
I guess it relates to X86_TRAP_BP. In entry_64.S:
.if \vector == X86_TRAP_BP /* * If coming from kernel space, create a 6-word gap to allow the * int3 handler to emulate a call instruction. */
> + > + wrmsrl(MSR_IA32_FRED_STKLVLS, > + FRED_STKLVL(X86_TRAP_DB, 1) | > + FRED_STKLVL(X86_TRAP_NMI, 2) | > + FRED_STKLVL(X86_TRAP_MC, 2) | > + FRED_STKLVL(X86_TRAP_DF, 3));
Why each exception here needs a stack level > 0? Especially for X86_TRAP_DB and X86_TRAP_NMI.
Why does or why does not X86_TRAP_VE have a stack level > 0?
X86_TRAP_DF is the highest stack level, is it accidental or deliberate?
Thanks Lai
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