Re: [PATCH v3 12/22] x86/traps: Introduce FRED entrypoints

[Jan Beulich <jbeulich@xxxxxxxx>]

On 04.10.2025 00:53, Andrew Cooper wrote:
> Under FRED, there's one entrypoint from Ring 3, and one from Ring 0.
> 
> FRED gives us a good stack (even for SYSCALL/SYSENTER), and a unified event
> frame on the stack, meaing that all software needs to do is spill the GPRs
> with a line of PUSHes.  Introduce PUSH_AND_CLEAR_GPRS and POP_GPRS for this
> purpose.
> 
> Introduce entry_FRED_R0() which to a first appoximation is complete for all
> event handling within Xen.
> 
> entry_FRED_R0() needs deriving from entry_FRED_R3(), so introduce a basic
> handler.  There is more work required to make the return-to-guest path work
> under FRED.
> 
> Also introduce entry_from_{xen,pv}() to be the C level handlers.  By simply
> copying regs->fred_ss.vector into regs->entry_vector, we can reuse all the
> existing fault handlers.
> 
> Extend fatal_trap() to render the event type, including by name, when FRED is
> active.  This is slightly complicated, because X86_ET_OTHER must not use
> vector_name() or SYSCALL and SYSENTER get rendered as #BP and #DB.
> 
> This is sufficient to handle all interrupts and exceptions encountered during
> development, including plenty of Double Faults.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>