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Fri, 09 Nov 2018 14:53:39 +0000 Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by userv0022.oracle.com (8.14.4/8.14.4) with ESMTP id wA9ErXTh002940 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 9 Nov 2018 14:53:33 GMT Received: from abhmp0001.oracle.com (abhmp0001.oracle.com [141.146.116.7]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id wA9ErWLw027102; Fri, 9 Nov 2018 14:53:32 GMT Received: from dhcp-burlington7-2nd-B-east-10-152-55-162.usdhcp.oraclecorp.com (/10.152.32.65) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Fri, 09 Nov 2018 06:53:32 -0800 Subject: Re: [PATCH] xen: fix xen_qlock_wait() To: Juergen Gross , linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, x86@kernel.org Cc: sstabellini@kernel.org, hpa@zytor.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, stable@vger.kernel.org References: <20181109120413.9539-1-jgross@suse.com> From: Boris Ostrovsky Openpgp: preference=signencrypt Autocrypt: addr=boris.ostrovsky@oracle.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.0 MIME-Version: 1.0 In-Reply-To: <20181109120413.9539-1-jgross@suse.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9071 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=878 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1807170000 definitions=main-1811090137 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/9/18 7:04 AM, Juergen Gross wrote: > Commit a856531951dc80 ("xen: make xen_qlock_wait() nestable") > introduced a regression for Xen guests running fully virtualized > (HVM or PVH mode). The Xen hypervisor wouldn't return from the poll > hypercall with interrupts disabled in case of an interrupt (for PV > guests it does). > > So instead of disabling interrupts in xen_qlock_wait() use a nesting > counter to avoid calling xen_clear_irq_pending() in case > xen_qlock_wait() is nested. > > Fixes: a856531951dc80 ("xen: make xen_qlock_wait() nestable") > Cc: stable@vger.kernel.org > Signed-off-by: Juergen Gross This needs Sander's Reported-by. > --- > arch/x86/xen/spinlock.c | 14 ++++++++------ > 1 file changed, 8 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c > index 441c88262169..1c8a8816a402 100644 > --- a/arch/x86/xen/spinlock.c > +++ b/arch/x86/xen/spinlock.c > @@ -9,6 +9,7 @@ > #include > #include > #include > +#include > > #include > #include > @@ -21,6 +22,7 @@ > > static DEFINE_PER_CPU(int, lock_kicker_irq) = -1; > static DEFINE_PER_CPU(char *, irq_name); > +static DEFINE_PER_CPU(atomic_t, xen_qlock_wait_nest); I'd move this to xen_qlock_wait(). Either way, Reviewed-by: Boris Ostrovsky > static bool xen_pvspin = true; > > static void xen_qlock_kick(int cpu) > @@ -39,25 +41,25 @@ static void xen_qlock_kick(int cpu) > */ > static void xen_qlock_wait(u8 *byte, u8 val) > { > - unsigned long flags; > int irq = __this_cpu_read(lock_kicker_irq); > + atomic_t *nest_cnt = this_cpu_ptr(&xen_qlock_wait_nest); > > /* If kicker interrupts not initialized yet, just spin */ > if (irq == -1 || in_nmi()) > return; > > - /* Guard against reentry. */ > - local_irq_save(flags); > + /* Detect reentry. */ > + atomic_inc(nest_cnt); > > - /* If irq pending already clear it. */ > - if (xen_test_irq_pending(irq)) { > + /* If irq pending already and no nested call clear it. */ > + if (atomic_read(nest_cnt) == 1 && xen_test_irq_pending(irq)) { > xen_clear_irq_pending(irq); > } else if (READ_ONCE(*byte) == val) { > /* Block until irq becomes pending (or a spurious wakeup) */ > xen_poll_irq(irq); > } > > - local_irq_restore(flags); > + atomic_dec(nest_cnt); > } > > static irqreturn_t dummy_handler(int irq, void *dev_id)