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Message-ID: <Y3yUdcJjrY2LhUWJ@hirez.programming.kicks-ass.net>
Date: Tue, 22 Nov 2022 10:20:53 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Kai Huang <kai.huang@...el.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
linux-mm@...ck.org, seanjc@...gle.com, pbonzini@...hat.com,
dave.hansen@...el.com, dan.j.williams@...el.com,
rafael.j.wysocki@...el.com, kirill.shutemov@...ux.intel.com,
ying.huang@...el.com, reinette.chatre@...el.com,
len.brown@...el.com, tony.luck@...el.com, ak@...ux.intel.com,
isaku.yamahata@...el.com, chao.gao@...el.com,
sathyanarayanan.kuppuswamy@...ux.intel.com, bagasdotme@...il.com,
sagis@...gle.com, imammedo@...hat.com
Subject: Re: [PATCH v7 06/20] x86/virt/tdx: Shut down TDX module in case of
error
On Mon, Nov 21, 2022 at 01:26:28PM +1300, Kai Huang wrote:
> Shutting down the TDX module requires calling TDH.SYS.LP.SHUTDOWN on all
> BIOS-enabled CPUs, and the SEMACALL can run concurrently on different
> CPUs. Implement a mechanism to run SEAMCALL concurrently on all online
> CPUs and use it to shut down the module. Later logical-cpu scope module
> initialization will use it too.
Uhh, those requirements ^ are not met by this:
> +static void seamcall_on_each_cpu(struct seamcall_ctx *sc)
> +{
> + on_each_cpu(seamcall_smp_call_function, sc, true);
> +}
Consider:
CPU0 CPU1 CPU2
local_irq_disable()
...
seamcall_on_each_cpu()
send-IPIs to 0 and 2
<IPI>
runs local seamcall
(seamcall done)
waits for 0 and 2
<has an NMI delay things>
runs seamcall
clears CSD_LOCK
</IPI>
... spinning ...
local_irq_enable()
<IPI>
runs seamcall
clears CSD_LOCK
*FINALLY* observes CSD_LOCK cleared on
all CPU and continues
</IPI>
IOW, they all 3 run seamcall at different times.
Either the Changelog is broken or this TDX crud is worse crap than I
thought possible, because the only way to actually meet that requirement
as stated is stop_machine().
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