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Wed, 08 Apr 2020 05:05:13 +0000 Received: from abhmp0012.oracle.com (abhmp0012.oracle.com [141.146.116.18]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 03855AVI015225; Wed, 8 Apr 2020 05:05:10 GMT Received: from monad.ca.oracle.com (/10.156.75.81) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 07 Apr 2020 22:05:09 -0700 From: Ankur Arora To: linux-kernel@vger.kernel.org, x86@kernel.org Subject: [RFC PATCH 09/26] x86/paravirt: Add runtime_patch() Date: Tue, 7 Apr 2020 22:03:06 -0700 Message-Id: <20200408050323.4237-10-ankur.a.arora@oracle.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200408050323.4237-1-ankur.a.arora@oracle.com> References: <20200408050323.4237-1-ankur.a.arora@oracle.com> MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9584 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 bulkscore=0 malwarescore=0 mlxlogscore=999 phishscore=0 spamscore=0 adultscore=0 suspectscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004080037 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9584 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 mlxlogscore=999 mlxscore=0 priorityscore=1501 bulkscore=0 adultscore=0 impostorscore=0 phishscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004080037 X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: jgross@suse.com, xen-devel@lists.xenproject.org, kvm@vger.kernel.org, peterz@infradead.org, hpa@zytor.com, Ankur Arora , virtualization@lists.linux-foundation.org, pbonzini@redhat.com, namit@vmware.com, mhiramat@kernel.org, jpoimboe@redhat.com, mihai.carabas@oracle.com, bp@alien8.de, vkuznets@redhat.com, boris.ostrovsky@oracle.com Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" runtime_patch() generates insn sequences for patching supported pv_ops. It does this by calling paravirt_patch_default() or native_patch() dpending on if the target is a paravirt or native pv-op. In addition, runtime_patch() also whitelists pv-ops that are safe to patch at runtime. The static conditions that need to be satisfied to patch safely: - Insn sequences under replacement need to execute without preemption. This is meant to avoid scenarios where a call-site (ex. lock.vcpu_is_preempted) switches between the following sequences: lock.vcpu_is_preempted = __raw_callee_save___kvm_vcpu_is_preempted 0: e8 31 e6 ff ff callq 0xffffffffffffe636 4: 66 90 xchg %ax,%ax # NOP2 lock.vcpu_is_preempted = __raw_callee_save___native_vcpu_is_preempted 0: 31 c0 xor %rax, %rax 2: 0f 1f 44 00 00 nopl 0x0(%rax) # NOP5 If kvm_vcpu_is_preempted() were preemptible, then, post patching we would return to address 4 above, which is in the middle of an instruction for native_vcpu_is_preempted(). Even if this were to be made safe (ex. by changing the NOP2 to be a prefix instead of a suffix), it would still not be enough -- since we do not want any code from the switched out pv-op to be executing after the pv-op has been switched out. - Entered only at the beginning: this allows us to use text_poke() which uses INT3 as a barrier. We don't store the address inside any call-sites so the second can be assumed. Guaranteeing the first condition boils down to stating that any pv-op being patched cannot be present/referenced from any call-stack in the system. pv-ops that are not obviously non-preemptible need to be enclosed in preempt_disable_runtime_patch()/preempt_enable_runtime_patch(). This should be sufficient because runtime_patch() itself is called from a stop_machine() context which would would be enough to flush out any non-preemptible sequences. Note that preemption in the host is okay: stop_machine() would unwind any pv-ops sleeping in the host. Signed-off-by: Ankur Arora --- arch/x86/include/asm/paravirt_types.h | 8 +++++ arch/x86/kernel/paravirt.c | 6 +--- arch/x86/kernel/paravirt_patch.c | 49 +++++++++++++++++++++++++++ include/linux/preempt.h | 17 ++++++++++ 4 files changed, 75 insertions(+), 5 deletions(-) diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h index bc935eec7ec6..3b9f6c105397 100644 --- a/arch/x86/include/asm/paravirt_types.h +++ b/arch/x86/include/asm/paravirt_types.h @@ -350,6 +350,12 @@ extern struct paravirt_patch_template native_pv_ops; #define PARAVIRT_PATCH(x) \ (offsetof(struct paravirt_patch_template, x) / sizeof(void *)) +/* + * Neat trick to map patch type back to the call within the + * corresponding structure. + */ +#define PARAVIRT_PATCH_OP(ops, type) (*(long *)(&((long **)&(ops))[type])) + #define paravirt_type(op) \ [paravirt_typenum] "i" (PARAVIRT_PATCH(op)), \ [paravirt_opptr] "i" (&(pv_ops.op)) @@ -383,6 +389,8 @@ unsigned paravirt_patch_default(u8 type, void *insn_buff, unsigned long addr, un unsigned paravirt_patch_insns(void *insn_buff, unsigned len, const char *start, const char *end); unsigned native_patch(u8 type, void *insn_buff, unsigned long addr, unsigned len); +int runtime_patch(u8 type, void *insn_buff, void *op, unsigned long addr, + unsigned int len); int paravirt_disable_iospace(void); diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c index 8c511cc4d4f4..c4128436b05a 100644 --- a/arch/x86/kernel/paravirt.c +++ b/arch/x86/kernel/paravirt.c @@ -117,11 +117,7 @@ void __init native_pv_lock_init(void) unsigned paravirt_patch_default(u8 type, void *insn_buff, unsigned long addr, unsigned len) { - /* - * Neat trick to map patch type back to the call within the - * corresponding structure. - */ - void *opfunc = *((void **)&pv_ops + type); + void *opfunc = (void *)PARAVIRT_PATCH_OP(pv_ops, type); unsigned ret; if (opfunc == NULL) diff --git a/arch/x86/kernel/paravirt_patch.c b/arch/x86/kernel/paravirt_patch.c index 3eff63c090d2..3eb8c0e720b4 100644 --- a/arch/x86/kernel/paravirt_patch.c +++ b/arch/x86/kernel/paravirt_patch.c @@ -1,5 +1,6 @@ // SPDX-License-Identifier: GPL-2.0 #include +#include #include #include @@ -124,3 +125,51 @@ unsigned int native_patch(u8 type, void *insn_buff, unsigned long addr, return paravirt_patch_default(type, insn_buff, addr, len); } + +#ifdef CONFIG_PARAVIRT_RUNTIME +/** + * runtime_patch - Generate patching code for a native/paravirt op + * @type: op type to generate code for + * @insn_buff: destination buffer + * @op: op target + * @addr: call site address + * @len: length of insn_buff + * + * Note that pv-ops are only suitable for runtime patching if they are + * non-preemptible. This is necessary for two reasons: we don't want to + * be overwriting insn sequences which might be referenced from call-stacks + * (and thus would be returned to), and we want patching to act as a barrier + * so no code from now stale paravirt ops should execute after an op has + * changed. + * + * Return: size of insn sequence on success, -EINVAL on error. + */ +int runtime_patch(u8 type, void *insn_buff, void *op, + unsigned long addr, unsigned int len) +{ + void *native_op; + int used = 0; + + /* Nothing whitelisted for now. */ + switch (type) { + default: + pr_warn("type=%d unsuitable for runtime-patching\n", type); + return -EINVAL; + } + + if (PARAVIRT_PATCH_OP(pv_ops, type) != (long)op) + PARAVIRT_PATCH_OP(pv_ops, type) = (long)op; + + native_op = (void *)PARAVIRT_PATCH_OP(native_pv_ops, type); + + /* + * Use native_patch() to get the right insns if we are switching + * back to a native_op. + */ + if (op == native_op) + used = native_patch(type, insn_buff, addr, len); + else + used = paravirt_patch_default(type, insn_buff, addr, len); + return used; +} +#endif /* CONFIG_PARAVIRT_RUNTIME */ diff --git a/include/linux/preempt.h b/include/linux/preempt.h index bc3f1aecaa19..c569d077aab2 100644 --- a/include/linux/preempt.h +++ b/include/linux/preempt.h @@ -203,6 +203,13 @@ do { \ __preempt_schedule(); \ } while (0) +/* + * preempt_enable_no_resched() so we don't add any preemption points until + * after the caller has returned. + */ +#define preempt_enable_runtime_patch() preempt_enable_no_resched() +#define preempt_disable_runtime_patch() preempt_disable() + #else /* !CONFIG_PREEMPTION */ #define preempt_enable() \ do { \ @@ -217,6 +224,12 @@ do { \ } while (0) #define preempt_check_resched() do { } while (0) + +/* + * NOP, if there's no preemption. + */ +#define preempt_disable_runtime_patch() do { } while (0) +#define preempt_enable_runtime_patch() do { } while (0) #endif /* CONFIG_PREEMPTION */ #define preempt_disable_notrace() \ @@ -250,6 +263,8 @@ do { \ #define preempt_enable_notrace() barrier() #define preemptible() 0 +#define preempt_disable_runtime_patch() do { } while (0) +#define preempt_enable_runtime_patch() do { } while (0) #endif /* CONFIG_PREEMPT_COUNT */ #ifdef MODULE @@ -260,6 +275,8 @@ do { \ #undef preempt_enable_no_resched #undef preempt_enable_no_resched_notrace #undef preempt_check_resched +#undef preempt_disable_runtime_patch +#undef preempt_enable_runtime_patch #endif #define preempt_set_need_resched() \