From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marc Zyngier Subject: Re: [PATCH v4 08/19] arm64: KVM: Dynamically patch the kernel/hyp VA mask Date: Thu, 15 Feb 2018 13:11:02 +0000 Message-ID: References: <20180104184334.16571-1-marc.zyngier@arm.com> <20180104184334.16571-9-marc.zyngier@arm.com> <20180115114719.GI21403@cbox> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, Mark Rutland , Catalin Marinas , Will Deacon , James Morse , Steve Capper , Peter Maydell To: Christoffer Dall Return-path: Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:53670 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030843AbeBONLG (ORCPT ); Thu, 15 Feb 2018 08:11:06 -0500 In-Reply-To: <20180115114719.GI21403@cbox> Content-Language: en-GB Sender: kvm-owner@vger.kernel.org List-ID: On 15/01/18 11:47, Christoffer Dall wrote: > On Thu, Jan 04, 2018 at 06:43:23PM +0000, Marc Zyngier wrote: >> So far, we're using a complicated sequence of alternatives to >> patch the kernel/hyp VA mask on non-VHE, and NOP out the >> masking altogether when on VHE. >> >> THe newly introduced dynamic patching gives us the opportunity > > nit: s/THe/The/ > >> to simplify that code by patching a single instruction with >> the correct mask (instead of the mind bending cummulative masking >> we have at the moment) or even a single NOP on VHE. >> >> Signed-off-by: Marc Zyngier >> --- >> arch/arm64/include/asm/kvm_mmu.h | 45 ++++++-------------- >> arch/arm64/kvm/Makefile | 2 +- >> arch/arm64/kvm/va_layout.c | 91 ++++++++++++++++++++++++++++++++++++++++ >> 3 files changed, 104 insertions(+), 34 deletions(-) >> create mode 100644 arch/arm64/kvm/va_layout.c >> >> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h >> index 672c8684d5c2..b0c3cbe9b513 100644 >> --- a/arch/arm64/include/asm/kvm_mmu.h >> +++ b/arch/arm64/include/asm/kvm_mmu.h >> @@ -69,9 +69,6 @@ >> * mappings, and none of this applies in that case. >> */ >> >> -#define HYP_PAGE_OFFSET_HIGH_MASK ((UL(1) << VA_BITS) - 1) >> -#define HYP_PAGE_OFFSET_LOW_MASK ((UL(1) << (VA_BITS - 1)) - 1) >> - >> #ifdef __ASSEMBLY__ >> >> #include >> @@ -81,28 +78,14 @@ >> * Convert a kernel VA into a HYP VA. >> * reg: VA to be converted. >> * >> - * This generates the following sequences: >> - * - High mask: >> - * and x0, x0, #HYP_PAGE_OFFSET_HIGH_MASK >> - * nop >> - * - Low mask: >> - * and x0, x0, #HYP_PAGE_OFFSET_HIGH_MASK >> - * and x0, x0, #HYP_PAGE_OFFSET_LOW_MASK >> - * - VHE: >> - * nop >> - * nop >> - * >> - * The "low mask" version works because the mask is a strict subset of >> - * the "high mask", hence performing the first mask for nothing. >> - * Should be completely invisible on any viable CPU. >> + * The actual code generation takes place in kvm_update_va_mask, and >> + * the instructions below are only there to reserve the space and >> + * perform the register allocation. > > Not just register allocation, but also to tell the generating code which > registers to use for its operands, right? That's what I meant by register allocation. > >> */ >> .macro kern_hyp_va reg >> -alternative_if_not ARM64_HAS_VIRT_HOST_EXTN >> - and \reg, \reg, #HYP_PAGE_OFFSET_HIGH_MASK >> -alternative_else_nop_endif >> -alternative_if ARM64_HYP_OFFSET_LOW >> - and \reg, \reg, #HYP_PAGE_OFFSET_LOW_MASK >> -alternative_else_nop_endif >> +alternative_cb kvm_update_va_mask >> + and \reg, \reg, #1 >> +alternative_cb_end >> .endm >> >> #else >> @@ -113,18 +96,14 @@ alternative_else_nop_endif >> #include >> #include >> >> +void kvm_update_va_mask(struct alt_instr *alt, >> + __le32 *origptr, __le32 *updptr, int nr_inst); >> + >> static inline unsigned long __kern_hyp_va(unsigned long v) >> { >> - asm volatile(ALTERNATIVE("and %0, %0, %1", >> - "nop", >> - ARM64_HAS_VIRT_HOST_EXTN) >> - : "+r" (v) >> - : "i" (HYP_PAGE_OFFSET_HIGH_MASK)); >> - asm volatile(ALTERNATIVE("nop", >> - "and %0, %0, %1", >> - ARM64_HYP_OFFSET_LOW) >> - : "+r" (v) >> - : "i" (HYP_PAGE_OFFSET_LOW_MASK)); >> + asm volatile(ALTERNATIVE_CB("and %0, %0, #1\n", >> + kvm_update_va_mask) >> + : "+r" (v)); >> return v; >> } >> >> diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile >> index 87c4f7ae24de..93afff91cb7c 100644 >> --- a/arch/arm64/kvm/Makefile >> +++ b/arch/arm64/kvm/Makefile >> @@ -16,7 +16,7 @@ kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/kvm_main.o $(KVM)/coalesced_mmio.o $(KVM)/e >> kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/arm.o $(KVM)/arm/mmu.o $(KVM)/arm/mmio.o >> kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/psci.o $(KVM)/arm/perf.o >> >> -kvm-$(CONFIG_KVM_ARM_HOST) += inject_fault.o regmap.o >> +kvm-$(CONFIG_KVM_ARM_HOST) += inject_fault.o regmap.o va_layout.o >> kvm-$(CONFIG_KVM_ARM_HOST) += hyp.o hyp-init.o handle_exit.o >> kvm-$(CONFIG_KVM_ARM_HOST) += guest.o debug.o reset.o sys_regs.o sys_regs_generic_v8.o >> kvm-$(CONFIG_KVM_ARM_HOST) += vgic-sys-reg-v3.o >> diff --git a/arch/arm64/kvm/va_layout.c b/arch/arm64/kvm/va_layout.c >> new file mode 100644 >> index 000000000000..aee758574e61 >> --- /dev/null >> +++ b/arch/arm64/kvm/va_layout.c >> @@ -0,0 +1,91 @@ >> +/* >> + * Copyright (C) 2017 ARM Ltd. >> + * Author: Marc Zyngier >> + * >> + * This program is free software; you can redistribute it and/or modify >> + * it under the terms of the GNU General Public License version 2 as >> + * published by the Free Software Foundation. >> + * >> + * This program is distributed in the hope that it will be useful, >> + * but WITHOUT ANY WARRANTY; without even the implied warranty of >> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the >> + * GNU General Public License for more details. >> + * >> + * You should have received a copy of the GNU General Public License >> + * along with this program. If not, see . >> + */ >> + >> +#include >> +#include >> +#include >> +#include >> +#include >> + >> +#define HYP_PAGE_OFFSET_HIGH_MASK ((UL(1) << VA_BITS) - 1) >> +#define HYP_PAGE_OFFSET_LOW_MASK ((UL(1) << (VA_BITS - 1)) - 1) >> + >> +static u64 va_mask; >> + >> +static void compute_layout(void) >> +{ >> + phys_addr_t idmap_addr = __pa_symbol(__hyp_idmap_text_start); >> + unsigned long mask = HYP_PAGE_OFFSET_HIGH_MASK; >> + >> + /* >> + * Activate the lower HYP offset only if the idmap doesn't >> + * clash with it, >> + */ > > The commentary is a bit strange given the logic below... > >> + if (idmap_addr > HYP_PAGE_OFFSET_LOW_MASK) >> + mask = HYP_PAGE_OFFSET_HIGH_MASK; > > ... was the initialization supposed to be LOW_MASK? > > (and does this imply that this was never tested on a system that > actually used the low mask?) I must has messed up with a later refactoring, as that code gets replaced pretty quickly in the series. The full series was definitely tested on Seattle with 39bit VAs, which is the only configuration I have that triggers the low mask. > >> + >> + va_mask = mask; >> +} >> + >> +static u32 compute_instruction(int n, u32 rd, u32 rn) >> +{ >> + u32 insn = AARCH64_BREAK_FAULT; >> + >> + switch (n) { >> + case 0: > > hmmm, wonder why we need this n==0 check... Makes patch splitting a bit easier. I can rework that if that helps. > >> + insn = aarch64_insn_gen_logical_immediate(AARCH64_INSN_LOGIC_AND, >> + AARCH64_INSN_VARIANT_64BIT, >> + rn, rd, va_mask); >> + break; >> + } >> + >> + return insn; >> +} >> + >> +void __init kvm_update_va_mask(struct alt_instr *alt, >> + __le32 *origptr, __le32 *updptr, int nr_inst) >> +{ >> + int i; >> + >> + /* We only expect a 1 instruction sequence */ > > nit: wording is a bit strange, how about > "We only expect a single instruction in the alternative sequence" Sure. > >> + BUG_ON(nr_inst != 1); >> + >> + if (!has_vhe() && !va_mask) >> + compute_layout(); >> + >> + for (i = 0; i < nr_inst; i++) { > > It's a bit funny to have a loop with the above BUG_ON. > > (I'm beginning to wonder if a future patch expands on this single > instruction thing, in which case a hint in the commit message would have > been nice.) That's indeed what is happening. A further patch expands the single instruction to a 5 instruction sequence. I'll add a comment to that effect. Thanks, M. -- Jazz is not dead. It just smells funny... From mboxrd@z Thu Jan 1 00:00:00 1970 From: marc.zyngier@arm.com (Marc Zyngier) Date: Thu, 15 Feb 2018 13:11:02 +0000 Subject: [PATCH v4 08/19] arm64: KVM: Dynamically patch the kernel/hyp VA mask In-Reply-To: <20180115114719.GI21403@cbox> References: <20180104184334.16571-1-marc.zyngier@arm.com> <20180104184334.16571-9-marc.zyngier@arm.com> <20180115114719.GI21403@cbox> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 15/01/18 11:47, Christoffer Dall wrote: > On Thu, Jan 04, 2018 at 06:43:23PM +0000, Marc Zyngier wrote: >> So far, we're using a complicated sequence of alternatives to >> patch the kernel/hyp VA mask on non-VHE, and NOP out the >> masking altogether when on VHE. >> >> THe newly introduced dynamic patching gives us the opportunity > > nit: s/THe/The/ > >> to simplify that code by patching a single instruction with >> the correct mask (instead of the mind bending cummulative masking >> we have at the moment) or even a single NOP on VHE. >> >> Signed-off-by: Marc Zyngier >> --- >> arch/arm64/include/asm/kvm_mmu.h | 45 ++++++-------------- >> arch/arm64/kvm/Makefile | 2 +- >> arch/arm64/kvm/va_layout.c | 91 ++++++++++++++++++++++++++++++++++++++++ >> 3 files changed, 104 insertions(+), 34 deletions(-) >> create mode 100644 arch/arm64/kvm/va_layout.c >> >> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h >> index 672c8684d5c2..b0c3cbe9b513 100644 >> --- a/arch/arm64/include/asm/kvm_mmu.h >> +++ b/arch/arm64/include/asm/kvm_mmu.h >> @@ -69,9 +69,6 @@ >> * mappings, and none of this applies in that case. >> */ >> >> -#define HYP_PAGE_OFFSET_HIGH_MASK ((UL(1) << VA_BITS) - 1) >> -#define HYP_PAGE_OFFSET_LOW_MASK ((UL(1) << (VA_BITS - 1)) - 1) >> - >> #ifdef __ASSEMBLY__ >> >> #include >> @@ -81,28 +78,14 @@ >> * Convert a kernel VA into a HYP VA. >> * reg: VA to be converted. >> * >> - * This generates the following sequences: >> - * - High mask: >> - * and x0, x0, #HYP_PAGE_OFFSET_HIGH_MASK >> - * nop >> - * - Low mask: >> - * and x0, x0, #HYP_PAGE_OFFSET_HIGH_MASK >> - * and x0, x0, #HYP_PAGE_OFFSET_LOW_MASK >> - * - VHE: >> - * nop >> - * nop >> - * >> - * The "low mask" version works because the mask is a strict subset of >> - * the "high mask", hence performing the first mask for nothing. >> - * Should be completely invisible on any viable CPU. >> + * The actual code generation takes place in kvm_update_va_mask, and >> + * the instructions below are only there to reserve the space and >> + * perform the register allocation. > > Not just register allocation, but also to tell the generating code which > registers to use for its operands, right? That's what I meant by register allocation. > >> */ >> .macro kern_hyp_va reg >> -alternative_if_not ARM64_HAS_VIRT_HOST_EXTN >> - and \reg, \reg, #HYP_PAGE_OFFSET_HIGH_MASK >> -alternative_else_nop_endif >> -alternative_if ARM64_HYP_OFFSET_LOW >> - and \reg, \reg, #HYP_PAGE_OFFSET_LOW_MASK >> -alternative_else_nop_endif >> +alternative_cb kvm_update_va_mask >> + and \reg, \reg, #1 >> +alternative_cb_end >> .endm >> >> #else >> @@ -113,18 +96,14 @@ alternative_else_nop_endif >> #include >> #include >> >> +void kvm_update_va_mask(struct alt_instr *alt, >> + __le32 *origptr, __le32 *updptr, int nr_inst); >> + >> static inline unsigned long __kern_hyp_va(unsigned long v) >> { >> - asm volatile(ALTERNATIVE("and %0, %0, %1", >> - "nop", >> - ARM64_HAS_VIRT_HOST_EXTN) >> - : "+r" (v) >> - : "i" (HYP_PAGE_OFFSET_HIGH_MASK)); >> - asm volatile(ALTERNATIVE("nop", >> - "and %0, %0, %1", >> - ARM64_HYP_OFFSET_LOW) >> - : "+r" (v) >> - : "i" (HYP_PAGE_OFFSET_LOW_MASK)); >> + asm volatile(ALTERNATIVE_CB("and %0, %0, #1\n", >> + kvm_update_va_mask) >> + : "+r" (v)); >> return v; >> } >> >> diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile >> index 87c4f7ae24de..93afff91cb7c 100644 >> --- a/arch/arm64/kvm/Makefile >> +++ b/arch/arm64/kvm/Makefile >> @@ -16,7 +16,7 @@ kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/kvm_main.o $(KVM)/coalesced_mmio.o $(KVM)/e >> kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/arm.o $(KVM)/arm/mmu.o $(KVM)/arm/mmio.o >> kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/psci.o $(KVM)/arm/perf.o >> >> -kvm-$(CONFIG_KVM_ARM_HOST) += inject_fault.o regmap.o >> +kvm-$(CONFIG_KVM_ARM_HOST) += inject_fault.o regmap.o va_layout.o >> kvm-$(CONFIG_KVM_ARM_HOST) += hyp.o hyp-init.o handle_exit.o >> kvm-$(CONFIG_KVM_ARM_HOST) += guest.o debug.o reset.o sys_regs.o sys_regs_generic_v8.o >> kvm-$(CONFIG_KVM_ARM_HOST) += vgic-sys-reg-v3.o >> diff --git a/arch/arm64/kvm/va_layout.c b/arch/arm64/kvm/va_layout.c >> new file mode 100644 >> index 000000000000..aee758574e61 >> --- /dev/null >> +++ b/arch/arm64/kvm/va_layout.c >> @@ -0,0 +1,91 @@ >> +/* >> + * Copyright (C) 2017 ARM Ltd. >> + * Author: Marc Zyngier >> + * >> + * This program is free software; you can redistribute it and/or modify >> + * it under the terms of the GNU General Public License version 2 as >> + * published by the Free Software Foundation. >> + * >> + * This program is distributed in the hope that it will be useful, >> + * but WITHOUT ANY WARRANTY; without even the implied warranty of >> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the >> + * GNU General Public License for more details. >> + * >> + * You should have received a copy of the GNU General Public License >> + * along with this program. If not, see . >> + */ >> + >> +#include >> +#include >> +#include >> +#include >> +#include >> + >> +#define HYP_PAGE_OFFSET_HIGH_MASK ((UL(1) << VA_BITS) - 1) >> +#define HYP_PAGE_OFFSET_LOW_MASK ((UL(1) << (VA_BITS - 1)) - 1) >> + >> +static u64 va_mask; >> + >> +static void compute_layout(void) >> +{ >> + phys_addr_t idmap_addr = __pa_symbol(__hyp_idmap_text_start); >> + unsigned long mask = HYP_PAGE_OFFSET_HIGH_MASK; >> + >> + /* >> + * Activate the lower HYP offset only if the idmap doesn't >> + * clash with it, >> + */ > > The commentary is a bit strange given the logic below... > >> + if (idmap_addr > HYP_PAGE_OFFSET_LOW_MASK) >> + mask = HYP_PAGE_OFFSET_HIGH_MASK; > > ... was the initialization supposed to be LOW_MASK? > > (and does this imply that this was never tested on a system that > actually used the low mask?) I must has messed up with a later refactoring, as that code gets replaced pretty quickly in the series. The full series was definitely tested on Seattle with 39bit VAs, which is the only configuration I have that triggers the low mask. > >> + >> + va_mask = mask; >> +} >> + >> +static u32 compute_instruction(int n, u32 rd, u32 rn) >> +{ >> + u32 insn = AARCH64_BREAK_FAULT; >> + >> + switch (n) { >> + case 0: > > hmmm, wonder why we need this n==0 check... Makes patch splitting a bit easier. I can rework that if that helps. > >> + insn = aarch64_insn_gen_logical_immediate(AARCH64_INSN_LOGIC_AND, >> + AARCH64_INSN_VARIANT_64BIT, >> + rn, rd, va_mask); >> + break; >> + } >> + >> + return insn; >> +} >> + >> +void __init kvm_update_va_mask(struct alt_instr *alt, >> + __le32 *origptr, __le32 *updptr, int nr_inst) >> +{ >> + int i; >> + >> + /* We only expect a 1 instruction sequence */ > > nit: wording is a bit strange, how about > "We only expect a single instruction in the alternative sequence" Sure. > >> + BUG_ON(nr_inst != 1); >> + >> + if (!has_vhe() && !va_mask) >> + compute_layout(); >> + >> + for (i = 0; i < nr_inst; i++) { > > It's a bit funny to have a loop with the above BUG_ON. > > (I'm beginning to wonder if a future patch expands on this single > instruction thing, in which case a hint in the commit message would have > been nice.) That's indeed what is happening. A further patch expands the single instruction to a 5 instruction sequence. I'll add a comment to that effect. Thanks, M. -- Jazz is not dead. It just smells funny...