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Fri, 31 Jan 2025 11:25:18 +0000 Received: from smtpav01.fra02v.mail.ibm.com (smtpav01.fra02v.mail.ibm.com [10.20.54.100]) by smtprelay05.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 50VBPF1M38338850 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 31 Jan 2025 11:25:15 GMT Received: from smtpav01.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 153E820138; Fri, 31 Jan 2025 11:25:15 +0000 (GMT) Received: from smtpav01.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9170320135; Fri, 31 Jan 2025 11:25:11 +0000 (GMT) Received: from p-imbrenda.ibmuc.com (unknown [9.171.25.38]) by smtpav01.fra02v.mail.ibm.com (Postfix) with ESMTP; Fri, 31 Jan 2025 11:25:11 +0000 (GMT) From: Claudio Imbrenda To: pbonzini@redhat.com Cc: kvm@vger.kernel.org, linux-s390@vger.kernel.org, frankja@linux.ibm.com, borntraeger@de.ibm.com, david@redhat.com Subject: [GIT PULL v2 03/20] KVM: s390: vsie: stop messing with page refcount Date: Fri, 31 Jan 2025 12:24:53 +0100 Message-ID: <20250131112510.48531-4-imbrenda@linux.ibm.com> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250131112510.48531-1-imbrenda@linux.ibm.com> References: <20250131112510.48531-1-imbrenda@linux.ibm.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: ot5_XRmuPvNH_3fWyzMFm3q1GjTUmT2T X-Proofpoint-ORIG-GUID: ot5_XRmuPvNH_3fWyzMFm3q1GjTUmT2T X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1057,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2025-01-31_04,2025-01-31_01,2024-11-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 malwarescore=0 lowpriorityscore=0 priorityscore=1501 suspectscore=0 clxscore=1015 mlxscore=0 spamscore=0 bulkscore=0 mlxlogscore=999 phishscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2501170000 definitions=main-2501310083 From: David Hildenbrand Let's stop messing with the page refcount, and use a flag that is set / cleared atomically to remember whether a vsie page is currently in use. Note that we could use a page flag, or a lower bit of the scb_gpa. Let's keep it simple for now, we have sufficient space. While at it, stop passing "struct kvm *" to put_vsie_page(), it's unused. Signed-off-by: David Hildenbrand Reviewed-by: Claudio Imbrenda Reviewed-by: Christoph Schlameuss Tested-by: Christoph Schlameuss Message-ID: <20250107154344.1003072-4-david@redhat.com> Signed-off-by: Claudio Imbrenda --- arch/s390/kvm/vsie.c | 46 +++++++++++++++++++++++++++++--------------- 1 file changed, 30 insertions(+), 16 deletions(-) diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c index 3874a1b49dd5..424f80f5f6b2 100644 --- a/arch/s390/kvm/vsie.c +++ b/arch/s390/kvm/vsie.c @@ -23,6 +23,10 @@ #include "kvm-s390.h" #include "gaccess.h" +enum vsie_page_flags { + VSIE_PAGE_IN_USE = 0, +}; + struct vsie_page { struct kvm_s390_sie_block scb_s; /* 0x0000 */ /* @@ -52,7 +56,12 @@ struct vsie_page { * radix tree. */ gpa_t scb_gpa; /* 0x0258 */ - __u8 reserved[0x0700 - 0x0260]; /* 0x0260 */ + /* + * Flags: must be set/cleared atomically after the vsie page can be + * looked up by other CPUs. + */ + unsigned long flags; /* 0x0260 */ + __u8 reserved[0x0700 - 0x0268]; /* 0x0268 */ struct kvm_s390_crypto_cb crycb; /* 0x0700 */ __u8 fac[S390_ARCH_FAC_LIST_SIZE_BYTE]; /* 0x0800 */ }; @@ -1351,6 +1360,20 @@ static int vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page) return rc; } +/* Try getting a given vsie page, returning "true" on success. */ +static inline bool try_get_vsie_page(struct vsie_page *vsie_page) +{ + if (test_bit(VSIE_PAGE_IN_USE, &vsie_page->flags)) + return false; + return !test_and_set_bit(VSIE_PAGE_IN_USE, &vsie_page->flags); +} + +/* Put a vsie page acquired through get_vsie_page / try_get_vsie_page. */ +static void put_vsie_page(struct vsie_page *vsie_page) +{ + clear_bit(VSIE_PAGE_IN_USE, &vsie_page->flags); +} + /* * Get or create a vsie page for a scb address. * @@ -1369,15 +1392,15 @@ static struct vsie_page *get_vsie_page(struct kvm *kvm, unsigned long addr) rcu_read_unlock(); if (page) { vsie_page = page_to_virt(page); - if (page_ref_inc_return(page) == 2) { + if (try_get_vsie_page(vsie_page)) { if (vsie_page->scb_gpa == addr) return vsie_page; /* * We raced with someone reusing + putting this vsie * page before we grabbed it. */ + put_vsie_page(vsie_page); } - page_ref_dec(page); } /* @@ -1394,7 +1417,7 @@ static struct vsie_page *get_vsie_page(struct kvm *kvm, unsigned long addr) return ERR_PTR(-ENOMEM); } vsie_page = page_to_virt(page); - page_ref_inc(page); + __set_bit(VSIE_PAGE_IN_USE, &vsie_page->flags); kvm->arch.vsie.pages[kvm->arch.vsie.page_count] = page; kvm->arch.vsie.page_count++; } else { @@ -1402,9 +1425,8 @@ static struct vsie_page *get_vsie_page(struct kvm *kvm, unsigned long addr) while (true) { page = kvm->arch.vsie.pages[kvm->arch.vsie.next]; vsie_page = page_to_virt(page); - if (page_ref_inc_return(page) == 2) + if (try_get_vsie_page(vsie_page)) break; - page_ref_dec(page); kvm->arch.vsie.next++; kvm->arch.vsie.next %= nr_vcpus; } @@ -1417,7 +1439,7 @@ static struct vsie_page *get_vsie_page(struct kvm *kvm, unsigned long addr) /* Double use of the same address or allocation failure. */ if (radix_tree_insert(&kvm->arch.vsie.addr_to_page, addr >> 9, page)) { - page_ref_dec(page); + put_vsie_page(vsie_page); mutex_unlock(&kvm->arch.vsie.mutex); return NULL; } @@ -1431,14 +1453,6 @@ static struct vsie_page *get_vsie_page(struct kvm *kvm, unsigned long addr) return vsie_page; } -/* put a vsie page acquired via get_vsie_page */ -static void put_vsie_page(struct kvm *kvm, struct vsie_page *vsie_page) -{ - struct page *page = pfn_to_page(__pa(vsie_page) >> PAGE_SHIFT); - - page_ref_dec(page); -} - int kvm_s390_handle_vsie(struct kvm_vcpu *vcpu) { struct vsie_page *vsie_page; @@ -1489,7 +1503,7 @@ int kvm_s390_handle_vsie(struct kvm_vcpu *vcpu) out_unpin_scb: unpin_scb(vcpu, vsie_page, scb_addr); out_put: - put_vsie_page(vcpu->kvm, vsie_page); + put_vsie_page(vsie_page); return rc < 0 ? rc : 0; }