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Thu, 14 Feb 2019 17:13:59 GMT Received: from [192.168.1.16] (/24.9.64.241) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Thu, 14 Feb 2019 09:13:58 -0800 Subject: Re: [RFC PATCH v8 03/14] mm, x86: Add support for eXclusive Page Frame Ownership (XPFO) To: Peter Zijlstra , juergh@gmail.com, jsteckli@amazon.de Cc: tycho@tycho.ws, ak@linux.intel.com, torvalds@linux-foundation.org, liran.alon@oracle.com, keescook@google.com, akpm@linux-foundation.org, mhocko@suse.com, catalin.marinas@arm.com, will.deacon@arm.com, jmorris@namei.org, konrad.wilk@oracle.com, Juerg Haefliger , deepa.srinivasan@oracle.com, chris.hyser@oracle.com, tyhicks@canonical.com, dwmw@amazon.co.uk, andrew.cooper3@citrix.com, jcm@redhat.com, boris.ostrovsky@oracle.com, kanth.ghatraju@oracle.com, oao.m.martins@oracle.com, jmattson@google.com, pradeep.vincent@oracle.com, john.haxby@oracle.com, tglx@linutronix.de, kirill.shutemov@linux.intel.com, hch@lst.de, steven.sistare@oracle.com, labbott@redhat.com, luto@kernel.org, dave.hansen@intel.com, kernel-hardening@lists.openwall.com, linux-mm@kvack.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Tycho Andersen , Marco Benatto References: <8275de2a7e6b72d19b1cd2ec5d71a42c2c7dd6c5.1550088114.git.khalid.aziz@oracle.com> <20190214105631.GJ32494@hirez.programming.kicks-ass.net> From: Khalid Aziz Organization: Oracle Corp Message-ID: Date: Thu, 14 Feb 2019 10:13:54 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <20190214105631.GJ32494@hirez.programming.kicks-ass.net> Content-Type: multipart/mixed; boundary="------------5EB9E0AEF4F8AD7EE9E16E15" Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9167 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1902140116 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: This is a multi-part message in MIME format. --------------5EB9E0AEF4F8AD7EE9E16E15 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 2/14/19 3:56 AM, Peter Zijlstra wrote: > On Wed, Feb 13, 2019 at 05:01:26PM -0700, Khalid Aziz wrote: >> static inline void *kmap_atomic(struct page *page) >> { >> + void *kaddr; >> + >> preempt_disable(); >> pagefault_disable(); >> + kaddr =3D page_address(page); >> + xpfo_kmap(kaddr, page); >> + return kaddr; >> } >> #define kmap_atomic_prot(page, prot) kmap_atomic(page) >> =20 >> static inline void __kunmap_atomic(void *addr) >> { >> + xpfo_kunmap(addr, virt_to_page(addr)); >> pagefault_enable(); >> preempt_enable(); >> } >=20 > How is that supposed to work; IIRC kmap_atomic was supposed to be > IRQ-safe. >=20 Ah, the spin_lock in in xpfo_kmap() can be problematic in interrupt context. I will see if I can fix that. Juerg, you wrote the original code and understand what you were trying to do here. If you have ideas on how to tackle this, I would very much appreciate it. >> +/* Per-page XPFO house-keeping data */ >> +struct xpfo { >> + unsigned long flags; /* Page state */ >> + bool inited; /* Map counter and lock initialized */ >=20 > What's sizeof(_Bool) ? Why can't you use a bit in that flags word? >=20 >> + atomic_t mapcount; /* Counter for balancing map/unmap requests */ >> + spinlock_t maplock; /* Lock to serialize map/unmap requests */ >> +}; >=20 > Without that bool, the structure would be 16 bytes on 64bit, which seem= s > like a good number. >=20 Patch 11 ("xpfo, mm: remove dependency on CONFIG_PAGE_EXTENSION") cleans all this up. If the original authors of these two patches, Juerg Haefliger and Julian Stecklina, are ok with it, I would like to combine the two patches in one. >> +void xpfo_kmap(void *kaddr, struct page *page) >> +{ >> + struct xpfo *xpfo; >> + >> + if (!static_branch_unlikely(&xpfo_inited)) >> + return; >> + >> + xpfo =3D lookup_xpfo(page); >> + >> + /* >> + * The page was allocated before page_ext was initialized (which mea= ns >> + * it's a kernel page) or it's allocated to the kernel, so nothing t= o >> + * do. >> + */ >> + if (!xpfo || unlikely(!xpfo->inited) || >> + !test_bit(XPFO_PAGE_USER, &xpfo->flags)) >> + return; >> + >> + spin_lock(&xpfo->maplock); >> + >> + /* >> + * The page was previously allocated to user space, so map it back >> + * into the kernel. No TLB flush required. >> + */ >> + if ((atomic_inc_return(&xpfo->mapcount) =3D=3D 1) && >> + test_and_clear_bit(XPFO_PAGE_UNMAPPED, &xpfo->flags)) >> + set_kpte(kaddr, page, PAGE_KERNEL); >> + >> + spin_unlock(&xpfo->maplock); >> +} >> +EXPORT_SYMBOL(xpfo_kmap); >> + >> +void xpfo_kunmap(void *kaddr, struct page *page) >> +{ >> + struct xpfo *xpfo; >> + >> + if (!static_branch_unlikely(&xpfo_inited)) >> + return; >> + >> + xpfo =3D lookup_xpfo(page); >> + >> + /* >> + * The page was allocated before page_ext was initialized (which mea= ns >> + * it's a kernel page) or it's allocated to the kernel, so nothing t= o >> + * do. >> + */ >> + if (!xpfo || unlikely(!xpfo->inited) || >> + !test_bit(XPFO_PAGE_USER, &xpfo->flags)) >> + return; >> + >> + spin_lock(&xpfo->maplock); >> + >> + /* >> + * The page is to be allocated back to user space, so unmap it from = the >> + * kernel, flush the TLB and tag it as a user page. >> + */ >> + if (atomic_dec_return(&xpfo->mapcount) =3D=3D 0) { >> + WARN(test_bit(XPFO_PAGE_UNMAPPED, &xpfo->flags), >> + "xpfo: unmapping already unmapped page\n"); >> + set_bit(XPFO_PAGE_UNMAPPED, &xpfo->flags); >> + set_kpte(kaddr, page, __pgprot(0)); >> + xpfo_flush_kernel_tlb(page, 0); >> + } >> + >> + spin_unlock(&xpfo->maplock); >> +} >> +EXPORT_SYMBOL(xpfo_kunmap); >=20 > And these here things are most definitely not IRQ-safe. >=20 Got it. I will work on this. 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