linux-kernel - Re: [PATCH v2 3/3] KVM: s390: Use generic VIRT_XFER_TO_GUEST

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Message-ID: <e76ed034-7c7a-4cd6-ae10-945ad39c2b00@linux.ibm.com>
Date: Thu, 27 Nov 2025 15:37:47 +0100
From: Janosch Frank <frankja@...ux.ibm.com>
To: Andrew Donnellan <ajd@...ux.ibm.com>, kvm@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Heiko Carstens
 <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>
Cc: Nicholas Miehlbradt <nicholas@...ux.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        David Hildenbrand <david@...nel.org>
Subject: Re: [PATCH v2 3/3] KVM: s390: Use generic VIRT_XFER_TO_GUEST_WORK
 functions

On 11/26/25 06:33, Andrew Donnellan wrote:
> Switch to using the generic infrastructure to check for and handle pending
> work before transitioning into guest mode.
> 
> xfer_to_guest_mode_handle_work() does a few more things than the current
> code does when deciding whether or not to exit the __vcpu_run() loop. The
> exittime tests from kvm-unit-tests, in my tests, were within a few percent
> compared to before this series, which is within noise tolerance.
> 
> Co-developed-by: Heiko Carstens <hca@...ux.ibm.com>
> Signed-off-by: Heiko Carstens <hca@...ux.ibm.com>
> Signed-off-by: Andrew Donnellan <ajd@...ux.ibm.com>
> ---
> v2: if work is handled, recheck for outstanding work with interrupts
>      disabled before entering guest (Heiko)
> 
> The way I've implemented this, I do the check between vcpu_pre_run() and
> entering the guest, and bail out of the loop if
> kvm_xfer_to_guest_mode_handle_work() returns nonzero, without calling
> vcpu_post_run(). My impression is that this is safe, but it does mean
> there is an sie_enter vcpu event and trace event which isn't matched with
> corresponding exit events. Is this a problem?


Acked-by: Janosch Frank <frankja@...ux.ibm.com>