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Re: [PATCH v2 20/23] x86/pv: Exception handling in FRED mode
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 1 Sep 2025 14:57:53 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Mon, 01 Sep 2025 12:58:04 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 28.08.2025 17:04, Andrew Cooper wrote:
> --- a/xen/arch/x86/traps.c
> +++ b/xen/arch/x86/traps.c
> @@ -2265,9 +2265,83 @@ void asmlinkage check_ist_exit(const struct
> cpu_user_regs *regs, bool ist_exit)
>
> void asmlinkage entry_from_pv(struct cpu_user_regs *regs)
> {
> + struct fred_info *fi = cpu_regs_fred_info(regs);
> + uint8_t type = regs->fred_ss.type;
> + uint8_t vec = regs->fred_ss.vector;
> +
> /* Copy fred_ss.vector into entry_vector as IDT delivery would have
> done. */
> - regs->entry_vector = regs->fred_ss.vector;
> + regs->entry_vector = vec;
> +
> + if ( !IS_ENABLED(CONFIG_PV) )
> + goto fatal;
> +
> + /*
> + * First, handle the asynchronous or fatal events. These are either
> + * unrelated to the interrupted context, or may not have valid context
> + * recorded, and all have special rules on how/whether to re-enable IRQs.
> + */
> + switch ( type )
> + {
> + case X86_ET_EXT_INTR:
> + return do_IRQ(regs);
>
> + case X86_ET_NMI:
> + return do_nmi(regs);
> +
> + case X86_ET_HW_EXC:
> + switch ( vec )
> + {
> + case X86_EXC_DF: return do_double_fault(regs);
> + case X86_EXC_MC: return do_machine_check(regs);
Looking at patch 21, I came to wonder where it is that we're moving back to
SL0 in the #MC case (which may not be fatal), for ERETU to not fault.
Jan
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