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Message-ID: <3bce15b2-c69c-4021-8b9e-0eba61487051@intel.com>
Date: Mon, 24 Jun 2024 16:53:59 -0700
From: Sohil Mehta <sohil.mehta@...el.com>
To: Jacob Pan <jacob.jun.pan@...ux.intel.com>, X86 Kernel <x86@...nel.org>,
LKML <linux-kernel@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>,
Dave Hansen <dave.hansen@...el.com>, "H. Peter Anvin" <hpa@...or.com>, "Ingo
Molnar" <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
<linux-perf-users@...r.kernel.org>, Peter Zijlstra <peterz@...radead.org>
CC: Andi Kleen <andi.kleen@...el.com>, Xin Li <xin3.li@...el.com>
Subject: Re: [PATCH v2 4/6] x86/irq: Process nmi sources in NMI handler
> + /*
> + * Per NMI source specification, there is no guarantee that a valid
> + * NMI vector is always delivered, even when the source specified
> + * one. It is software's responsibility to check all available NMI
> + * sources when bit 0 is set in the NMI source bitmap. i.e. we have
> + * to call every handler as if we have no NMI source.
> + * On the other hand, if we do get non-zero vectors, we know exactly
> + * what the sources are. So we only call the handlers with the bit set.
> + */
The use of "we" here can be a bit confusing. Writing this in an
imperative mood might make it easier to follow.
> + if (source_bitmask & BIT(NMI_SOURCE_VEC_UNKNOWN)) {
> + pr_warn_ratelimited("NMI received with unknown source\n");
> + return 0;
> + }
> +
IIUC, bit 0 will be set for out of bounds vectors (>= 16 bit) as well. I
am not sure how realistic that is or if that is even possible to detect?
I am wondering if there should an explicit error message when such a
scenario happens.
> + rcu_read_lock();
> + /* Bit 0 is for unknown NMI sources, skip it. */
> + for_each_set_bit_from(vec, &source_bitmask, NR_NMI_SOURCE_VECTORS) {
> + a = rcu_dereference(nmiaction_src_table[vec]);
> + if (!a) {
> + pr_warn_ratelimited("NMI received %d no handler", vec);
> + continue;
> + }
> + handled += do_handle_nmi(a, regs, type);
> + }
> + rcu_read_unlock();
> + return handled;
> +}
> +
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