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[192.237.175.120]) by mx.google.com with ESMTPS id o66si3310931yba.405.2018.12.04.12.29.06 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 04 Dec 2018 12:29:06 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of xen-devel-bounces@lists.xenproject.org designates 192.237.175.120 as permitted sender) client-ip=192.237.175.120; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of xen-devel-bounces@lists.xenproject.org designates 192.237.175.120 as permitted sender) smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1gUHI9-0008Jf-HB; Tue, 04 Dec 2018 20:27:37 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1gUHI7-0008Gl-R7 for xen-devel@lists.xenproject.org; Tue, 04 Dec 2018 20:27:35 +0000 X-Inumbo-ID: 08a6f9f8-f803-11e8-9411-43a526868f8e Received: from foss.arm.com (unknown [217.140.101.70]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTP id 08a6f9f8-f803-11e8-9411-43a526868f8e; Tue, 04 Dec 2018 20:27:34 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A639015BE; Tue, 4 Dec 2018 12:27:34 -0800 (PST) Received: from e108454-lin.cambridge.arm.com (e108454-lin.cambridge.arm.com [10.1.196.50]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B12E73F614; Tue, 4 Dec 2018 12:27:33 -0800 (PST) From: Julien Grall To: xen-devel@lists.xenproject.org Date: Tue, 4 Dec 2018 20:26:50 +0000 Message-Id: <20181204202651.8836-17-julien.grall@arm.com> X-Mailer: git-send-email 2.11.0 In-Reply-To: <20181204202651.8836-1-julien.grall@arm.com> References: <20181204202651.8836-1-julien.grall@arm.com> Subject: [Xen-devel] [PATCH for-4.12 v2 16/17] xen/arm: Implement Set/Way operations 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: Julien Grall , sstabellini@kernel.org MIME-Version: 1.0 Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" Set/Way operations are used to perform maintenance on a given cache. At the moment, Set/Way operations are not trapped and therefore a guest OS will directly act on the local cache. However, a vCPU may migrate to another pCPU in the middle of the processor. This will result to have cache with stall data (Set/Way are not propagated) potentially causing crash. This may be the cause of heisenbug noticed in Osstest [1]. Furthermore, Set/Way operations are not available on system cache. This means that OS, such as Linux 32-bit, relying on those operations to fully clean the cache before disabling MMU may break because data may sits in system caches and not in RAM. For more details about Set/Way, see the talk "The Art of Virtualizing Cache Maintenance" given at Xen Summit 2018 [2]. In the context of Xen, we need to trap Set/Way operations and emulate them. From the Arm Arm (B1.14.4 in DDI 046C.c), Set/Way operations are difficult to virtualized. So we can assume that a guest OS using them will suffer the consequence (i.e slowness) until developer removes all the usage of Set/Way. As the software is not allowed to infer the Set/Way to Physical Address mapping, Xen will need to go through the guest P2M and clean & invalidate all the entries mapped. Because Set/Way happen in batch (a loop on all Set/Way of a cache), Xen would need to go through the P2M for every instructions. This is quite expensive and would severely impact the guest OS. The implementation is re-using the KVM policy to limit the number of flush: - If we trap a Set/Way operations, we enable VM trapping (i.e HVC_EL2.TVM) to detect cache being turned on/off, and do a full clean. - We clean the caches when turning on and off - Once the caches are enabled, we stop trapping VM instructions [1] https://lists.xenproject.org/archives/html/xen-devel/2017-09/msg03191.html [2] https://fr.slideshare.net/xen_com_mgr/virtualizing-cache Signed-off-by: Julien Grall --- Changes in v2: - Fix emulation for Set/Way cache flush arm64 sysreg - Add support for preemption - Check cache status on every VM traps in Arm64 - Remove spurious change --- xen/arch/arm/arm64/vsysreg.c | 17 ++++++++ xen/arch/arm/p2m.c | 92 ++++++++++++++++++++++++++++++++++++++++++++ xen/arch/arm/traps.c | 25 +++++++++++- xen/arch/arm/vcpreg.c | 22 +++++++++++ xen/include/asm-arm/domain.h | 8 ++++ xen/include/asm-arm/p2m.h | 20 ++++++++++ 6 files changed, 183 insertions(+), 1 deletion(-) diff --git a/xen/arch/arm/arm64/vsysreg.c b/xen/arch/arm/arm64/vsysreg.c index 16ac9c344a..8a85507d9d 100644 --- a/xen/arch/arm/arm64/vsysreg.c +++ b/xen/arch/arm/arm64/vsysreg.c @@ -34,9 +34,14 @@ static bool vreg_emulate_##reg(struct cpu_user_regs *regs, \ uint64_t *r, bool read) \ { \ + struct vcpu *v = current; \ + bool cache_enabled = vcpu_has_cache_enabled(v); \ + \ GUEST_BUG_ON(read); \ WRITE_SYSREG64(*r, reg); \ \ + p2m_toggle_cache(v, cache_enabled); \ + \ return true; \ } @@ -85,6 +90,18 @@ void do_sysreg(struct cpu_user_regs *regs, break; /* + * HCR_EL2.TSW + * + * ARMv8 (DDI 0487B.b): Table D1-42 + */ + case HSR_SYSREG_DCISW: + case HSR_SYSREG_DCCSW: + case HSR_SYSREG_DCCISW: + if ( !hsr.sysreg.read ) + p2m_set_way_flush(current); + break; + + /* * HCR_EL2.TVM * * ARMv8 (DDI 0487D.a): Table D1-38 diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c index ca9f0d9ebe..8ee6ff7bd7 100644 --- a/xen/arch/arm/p2m.c +++ b/xen/arch/arm/p2m.c @@ -3,6 +3,7 @@ #include #include #include +#include #include #include @@ -1620,6 +1621,97 @@ int p2m_cache_flush_range(struct domain *d, gfn_t *pstart, gfn_t end) return rc; } +/* + * Clean & invalidate RAM associated to the guest vCPU. + * + * The function can only work with the current vCPU and should be called + * with IRQ enabled as the vCPU could get preempted. + */ +void p2m_flush_vm(struct vcpu *v) +{ + int rc; + gfn_t start = _gfn(0); + + ASSERT(v == current); + ASSERT(local_irq_is_enabled()); + ASSERT(v->arch.need_flush_to_ram); + + do + { + rc = p2m_cache_flush_range(v->domain, &start, _gfn(ULONG_MAX)); + if ( rc == -ERESTART ) + do_softirq(); + } while ( rc == -ERESTART ); + + if ( rc != 0 ) + gprintk(XENLOG_WARNING, + "P2M has not been correctly cleaned (rc = %d)\n", + rc); + + v->arch.need_flush_to_ram = false; +} + +/* + * See note at ARMv7 ARM B1.14.4 (DDI 0406C.c) (TL;DR: S/W ops are not + * easily virtualized). + * + * Main problems: + * - S/W ops are local to a CPU (not broadcast) + * - We have line migration behind our back (speculation) + * - System caches don't support S/W at all (damn!) + * + * In the face of the above, the best we can do is to try and convert + * S/W ops to VA ops. Because the guest is not allowed to infer the S/W + * to PA mapping, it can only use S/W to nuke the whole cache, which is + * rather a good thing for us. + * + * Also, it is only used when turning caches on/off ("The expected + * usage of the cache maintenance instructions that operate by set/way + * is associated with the powerdown and powerup of caches, if this is + * required by the implementation."). + * + * We use the following policy: + * - If we trap a S/W operation, we enabled VM trapping to detect + * caches being turned on/off, and do a full clean. + * + * - We flush the caches on both caches being turned on and off. + * + * - Once the caches are enabled, we stop trapping VM ops. + */ +void p2m_set_way_flush(struct vcpu *v) +{ + /* This function can only work with the current vCPU. */ + ASSERT(v == current); + + if ( !(v->arch.hcr_el2 & HCR_TVM) ) + { + v->arch.need_flush_to_ram = true; + vcpu_hcr_set_flags(v, HCR_TVM); + } +} + +void p2m_toggle_cache(struct vcpu *v, bool was_enabled) +{ + bool now_enabled = vcpu_has_cache_enabled(v); + + /* This function can only work with the current vCPU. */ + ASSERT(v == current); + + /* + * If switching the MMU+caches on, need to invalidate the caches. + * If switching it off, need to clean the caches. + * Clean + invalidate does the trick always. + */ + if ( was_enabled != now_enabled ) + { + v->arch.need_flush_to_ram = true; + } + + /* Caches are now on, stop trapping VM ops (until a S/W op) */ + if ( now_enabled ) + vcpu_hcr_clear_flags(v, HCR_TVM); +} + mfn_t gfn_to_mfn(struct domain *d, gfn_t gfn) { return p2m_lookup(d, gfn, NULL); diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c index 02665cc7b4..221c762ada 100644 --- a/xen/arch/arm/traps.c +++ b/xen/arch/arm/traps.c @@ -97,7 +97,7 @@ register_t get_default_hcr_flags(void) { return (HCR_PTW|HCR_BSU_INNER|HCR_AMO|HCR_IMO|HCR_FMO|HCR_VM| (vwfi != NATIVE ? (HCR_TWI|HCR_TWE) : 0) | - HCR_TSC|HCR_TAC|HCR_SWIO|HCR_TIDCP|HCR_FB); + HCR_TSC|HCR_TAC|HCR_SWIO|HCR_TIDCP|HCR_FB|HCR_TSW); } static enum { @@ -2258,10 +2258,33 @@ static void check_for_pcpu_work(void) } } +/* + * Process pending work for the vCPU. Any call should be fast or + * implement preemption. + */ +static void check_for_vcpu_work(void) +{ + struct vcpu *v = current; + + if ( likely(!v->arch.need_flush_to_ram) ) + return; + + /* + * Give a chance for the pCPU to process work before handling the vCPU + * pending work. + */ + check_for_pcpu_work(); + + local_irq_enable(); + p2m_flush_vm(v); + local_irq_disable(); +} + void leave_hypervisor_tail(void) { local_irq_disable(); + check_for_vcpu_work(); check_for_pcpu_work(); vgic_sync_to_lrs(); diff --git a/xen/arch/arm/vcpreg.c b/xen/arch/arm/vcpreg.c index 550c25ec3f..cdc91cdf5b 100644 --- a/xen/arch/arm/vcpreg.c +++ b/xen/arch/arm/vcpreg.c @@ -51,9 +51,14 @@ #define TVM_REG(sz, func, reg...) \ static bool func(struct cpu_user_regs *regs, uint##sz##_t *r, bool read) \ { \ + struct vcpu *v = current; \ + bool cache_enabled = vcpu_has_cache_enabled(v); \ + \ GUEST_BUG_ON(read); \ WRITE_SYSREG##sz(*r, reg); \ \ + p2m_toggle_cache(v, cache_enabled); \ + \ return true; \ } @@ -71,6 +76,8 @@ static bool func(struct cpu_user_regs *regs, uint##sz##_t *r, bool read) \ static bool vreg_emulate_##xreg(struct cpu_user_regs *regs, uint32_t *r, \ bool read, bool hi) \ { \ + struct vcpu *v = current; \ + bool cache_enabled = vcpu_has_cache_enabled(v); \ register_t reg = READ_SYSREG(xreg); \ \ GUEST_BUG_ON(read); \ @@ -86,6 +93,8 @@ static bool vreg_emulate_##xreg(struct cpu_user_regs *regs, uint32_t *r, \ } \ WRITE_SYSREG(reg, xreg); \ \ + p2m_toggle_cache(v, cache_enabled); \ + \ return true; \ } \ \ @@ -186,6 +195,19 @@ void do_cp15_32(struct cpu_user_regs *regs, const union hsr hsr) break; /* + * HCR_EL2.TSW + * + * ARMv7 (DDI 0406C.b): B1.14.6 + * ARMv8 (DDI 0487B.b): Table D1-42 + */ + case HSR_CPREG32(DCISW): + case HSR_CPREG32(DCCSW): + case HSR_CPREG32(DCCISW): + if ( !cp32.read ) + p2m_set_way_flush(current); + break; + + /* * HCR_EL2.TVM * * ARMv8 (DDI 0487D.a): Table D1-38 diff --git a/xen/include/asm-arm/domain.h b/xen/include/asm-arm/domain.h index 175de44927..f16b973e0d 100644 --- a/xen/include/asm-arm/domain.h +++ b/xen/include/asm-arm/domain.h @@ -202,6 +202,14 @@ struct arch_vcpu struct vtimer phys_timer; struct vtimer virt_timer; bool vtimer_initialized; + + /* + * The full P2M may require some cleaning (e.g when emulation + * set/way). As the action can take a long time, it requires + * preemption. So this is deferred until we return to the guest. + */ + bool need_flush_to_ram; + } __cacheline_aligned; void vcpu_show_execution_state(struct vcpu *); diff --git a/xen/include/asm-arm/p2m.h b/xen/include/asm-arm/p2m.h index a633e27cc9..79abcb5a63 100644 --- a/xen/include/asm-arm/p2m.h +++ b/xen/include/asm-arm/p2m.h @@ -6,6 +6,8 @@ #include #include +#include + #define paddr_bits PADDR_BITS /* Holds the bit size of IPAs in p2m tables. */ @@ -237,6 +239,12 @@ bool p2m_resolve_translation_fault(struct domain *d, gfn_t gfn); */ int p2m_cache_flush_range(struct domain *d, gfn_t *pstart, gfn_t end); +void p2m_set_way_flush(struct vcpu *v); + +void p2m_toggle_cache(struct vcpu *v, bool was_enabled); + +void p2m_flush_vm(struct vcpu *v); + /* * Map a region in the guest p2m with a specific p2m type. * The memory attributes will be derived from the p2m type. @@ -364,6 +372,18 @@ static inline int set_foreign_p2m_entry(struct domain *d, unsigned long gfn, return -EOPNOTSUPP; } +/* + * A vCPU has cache enabled only when the MMU is enabled and data cache + * is enabled. + */ +static inline bool vcpu_has_cache_enabled(struct vcpu *v) +{ + /* Only works with the current vCPU */ + ASSERT(current == v); + + return (READ_SYSREG32(SCTLR_EL1) & (SCTLR_C|SCTLR_M)) == (SCTLR_C|SCTLR_M); +} + #endif /* _XEN_P2M_H */ /*