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Mon, 6 Mar 2023 18:18:12 GMT Received: from smtpav04.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 4E74F2004E; Mon, 6 Mar 2023 18:18:12 +0000 (GMT) Received: from smtpav04.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 31A4620040; Mon, 6 Mar 2023 18:18:11 +0000 (GMT) Received: from thinkpad (unknown [9.171.75.232]) by smtpav04.fra02v.mail.ibm.com (Postfix) with SMTP; Mon, 6 Mar 2023 18:18:11 +0000 (GMT) Date: Mon, 6 Mar 2023 19:18:09 +0100 From: Gerald Schaefer To: Catalin Marinas Cc: Andrew Morton , David Hildenbrand , Matthew Wilcox , Anshuman Khandual , Will Deacon , Thomas Bogendoerfer , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Alexander Gordeev , linux-mips , linux-power , linux-x86 , linux-s390 , LKML , linux-mm Subject: Re: [PATCH] mm: add PTE pointer parameter to flush_tlb_fix_spurious_fault() Message-ID: <20230306191809.77144eec@thinkpad> In-Reply-To: References: <20230306161548.661740-1-gerald.schaefer@linux.ibm.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.36; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: Q6RU0_1d33mcmcSdtwyO-VmlbiReyfsE X-Proofpoint-GUID: PmcJFWFlbELOtLm7Z0Wo3Lyr_EPiLECW X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.219,Aquarius:18.0.942,Hydra:6.0.573,FMLib:17.11.170.22 definitions=2023-03-06_11,2023-03-06_01,2023-02-09_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 impostorscore=0 lowpriorityscore=0 malwarescore=0 bulkscore=0 clxscore=1015 suspectscore=0 mlxlogscore=937 mlxscore=0 priorityscore=1501 adultscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2212070000 definitions=main-2303060156 X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: z7998yit8go54jgg6jwrez8kj4tbkwwc X-Rspamd-Queue-Id: CCC1B100005 X-HE-Tag: 1678126723-2731 X-HE-Meta: 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 yttzGYAg /8Y9VGkau6FXQ3wCPGiFljlrfVkdLL+DAWSkfPWwx62i46OK7dfBZ004NxIALRPu/KoradFS3Oj9Gie7mNe45ZtWbCzZwZwFNGPGGf55ntk1Kg6/9qc1g1IWSVs0VztlTKT7kgJaIyaf6zKNXPT263j02hZV3+RTKkyALeYtxOSu3xBrsEKRtBu0lTGQUk0aZfxS6qlwp40E75UXoJX99fG2iaj+W16xC9rJL9irII88U/fVOKtth2wkw3Ef8G4s4yjmI X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, 6 Mar 2023 17:06:44 +0000 Catalin Marinas wrote: > On Mon, Mar 06, 2023 at 05:15:48PM +0100, Gerald Schaefer wrote: > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > > index b6ba466e2e8a..0bd18de9fd97 100644 > > --- a/arch/arm64/include/asm/pgtable.h > > +++ b/arch/arm64/include/asm/pgtable.h > > @@ -57,7 +57,7 @@ static inline bool arch_thp_swp_supported(void) > > * fault on one CPU which has been handled concurrently by another CPU > > * does not need to perform additional invalidation. > > */ > > -#define flush_tlb_fix_spurious_fault(vma, address) do { } while (0) > > +#define flush_tlb_fix_spurious_fault(vma, address, ptep) do { } while (0) > > For arm64: > > Acked-by: Catalin Marinas > > > diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h > > index 2c70b4d1263d..c1f6b46ec555 100644 > > --- a/arch/s390/include/asm/pgtable.h > > +++ b/arch/s390/include/asm/pgtable.h > > @@ -1239,7 +1239,8 @@ static inline int pte_allow_rdp(pte_t old, pte_t new) > > } > > > > static inline void flush_tlb_fix_spurious_fault(struct vm_area_struct *vma, > > - unsigned long address) > > + unsigned long address, > > + pte_t *ptep) > > { > > /* > > * RDP might not have propagated the PTE protection reset to all CPUs, > > @@ -1247,11 +1248,12 @@ static inline void flush_tlb_fix_spurious_fault(struct vm_area_struct *vma, > > * NOTE: This will also be called when a racing pagetable update on > > * another thread already installed the correct PTE. Both cases cannot > > * really be distinguished. > > - * Therefore, only do the local TLB flush when RDP can be used, to avoid > > - * unnecessary overhead. > > + * Therefore, only do the local TLB flush when RDP can be used, and the > > + * PTE does not have _PAGE_PROTECT set, to avoid unnecessary overhead. > > + * A local RDP can be used to do the flush. > > */ > > - if (MACHINE_HAS_RDP) > > - asm volatile("ptlb" : : : "memory"); > > + if (MACHINE_HAS_RDP && !(pte_val(*ptep) & _PAGE_PROTECT)) > > + __ptep_rdp(address, ptep, 0, 0, 1); > > I wonder whether passing the actual entry is somewhat quicker as it > avoids another memory access (though it might already be in the cache). The RDP instruction itself only requires the PTE pointer as input, or more precisely a pointer to the pagetable origin. We calculate that from the PTE pointer, by masking out some bits, w/o actual memory access to the PTE entry value. Of course, there is the pte_val(*ptep) & _PAGE_PROTECT check here, with memory access, but this might get removed in the future. TBH, I simply wasn't sure (enough) yet, if we could technically ever end up here with _PAGE_PROTECT set at all. For "real" spurious protection faults, it should never be set, not so sure about racing pagetable updates though. So this might actually be an unnecessary / overly cautious check, that gets removed in the future, and not worth passing along the PTE value in addition to the pointer.