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From: Thomas Gleixner <tglx@linutronix.de>
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To: Sean Christopherson <seanjc@google.com>
Cc: LKML <linux-kernel@vger.kernel.org>, Michael Jeanson
 <mjeanson@efficios.com>, Jens Axboe <axboe@kernel.dk>, Paolo Bonzini
 <pbonzini@redhat.com>, Wei Liu <wei.liu@kernel.org>, Dexuan Cui
 <decui@microsoft.com>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
 Peter Zijlstra <peterz@infradead.org>, "Paul E. McKenney"
 <paulmck@kernel.org>, Boqun Feng <boqun.feng@gmail.com>, x86@kernel.org,
 Arnd Bergmann <arnd@arndb.de>, Heiko Carstens <hca@linux.ibm.com>,
 Christian Borntraeger <borntraeger@linux.ibm.com>, Sven Schnelle
 <svens@linux.ibm.com>, Huacai Chen <chenhuacai@kernel.org>, Paul Walmsley
 <paul.walmsley@sifive.com>, Palmer Dabbelt <palmer@dabbelt.com>
Subject: Re: [patch V4 07/36] rseq, virt: Retrigger RSEQ after vcpu_run()
In-Reply-To: <aL9uLYpUcOA9Jt4q@google.com>
References: <20250908212737.353775467@linutronix.de>
 <20250908212925.708769718@linutronix.de> <aL9uLYpUcOA9Jt4q@google.com>
Date: Tue, 09 Sep 2025 14:10:49 +0200
Message-ID: <87y0qnvnau.ffs@tglx>
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On Mon, Sep 08 2025 at 17:00, Sean Christopherson wrote:
> On Mon, Sep 08, 2025, Thomas Gleixner wrote:
>> --- a/virt/kvm/kvm_main.c
>> +++ b/virt/kvm/kvm_main.c
>> @@ -49,6 +49,7 @@
>>  #include <linux/lockdep.h>
>>  #include <linux/kthread.h>
>>  #include <linux/suspend.h>
>> +#include <linux/rseq.h>
>>  
>>  #include <asm/processor.h>
>>  #include <asm/ioctl.h>
>> @@ -4466,6 +4467,8 @@ static long kvm_vcpu_ioctl(struct file *
>>  		r = kvm_arch_vcpu_ioctl_run(vcpu);
>>  		vcpu->wants_to_run = false;
>>  
>
> Finally had a lightbulb moment as to how to eat this hack while not stonewalling
> the entire series.  Can you add something like:
>
> 		/*
> 		 * FIXME: Remove this hack once all KVM architectures support
> 		 * the generic TIF bits, i.e. a dedicated TIF_RSEQ.
> 		 */
>
> to discourage further abuse, and to make it clear that such ugliness isn't anyone's
> first choice.  With that,

Fair enough.