Messages in this thread | | | Date | Wed, 17 Apr 2024 11:38:13 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH v3 1/1] x86/fred: Fix INT80 emulation for FRED |
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On Tue, Apr 16, 2024 at 11:30:01PM -0700, Xin Li (Intel) wrote: > 3) The FRED kernel entry handler does *NOT* dispatch INT instructions, > which is of event type EVENT_TYPE_SWINT, so compared with > do_int80_emulation(), there is no need to do any user mode check.
What does that mean?
An event handler doesn't dispatch INT insns?
/me is confused.
> +#ifdef CONFIG_X86_FRED > +/* > + * A FRED-specific INT80 handler fred_int80_emulation() is required: > + * > + * 1) As INT instructions and hardware interrupts are separate event > + * types, FRED does not preclude the use of vector 0x80 for external > + * interrupts. As a result the FRED setup code does *NOT* reserve > + * vector 0x80 and calling int80_is_external() is not merely > + * suboptimal but actively incorrect: it could cause a system call > + * to be incorrectly ignored. > + * > + * 2) fred_int80_emulation(), only called for handling vector 0x80 of > + * event type EVENT_TYPE_SWINT, will NEVER be called to handle any > + * external interrupt (event type EVENT_TYPE_EXTINT). > + * > + * 3) The FRED kernel entry handler does *NOT* dispatch INT instructions, > + * which is of event type EVENT_TYPE_SWINT, so compared with > + * do_int80_emulation(), there is no need to do any user mode check. > + * > + * 4) int80_emulation() does a CLEAR_BRANCH_HISTORY, which is likely > + * overkill for new x86 CPU implementations that support FRED. > + * > + * 5) int $0x80 is the FAST path for 32-bit system calls under FRED. > + * > + * A dedicated FRED INT80 handler duplicates quite a bit of the code in > + * do_int80_emulation(), but it avoids sprinkling more tests and seems > + * more readable. Just remember that we can always unify common stuff > + * later if it turns out that it won't diverge anymore, i.e., after the > + * FRED code settles. > + */
And this is talking about duplication above and that text is duplicated from the commit message. :)
I'll zap it when applying.
Thx.
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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