From: Atish Patra <atishp@rivosinc.com> To: Andrew Jones <ajones@ventanamicro.com> Cc: linux-kernel@vger.kernel.org, Anup Patel <anup@brainfault.org>, Ajay Kaher <akaher@vmware.com>, Alexandre Ghiti <alexghiti@rivosinc.com>, Alexey Makhalov <amakhalov@vmware.com>, Conor Dooley <conor.dooley@microchip.com>, Juergen Gross <jgross@suse.com>, kvm-riscv@lists.infradead.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-riscv@lists.infradead.org, Mark Rutland <mark.rutland@arm.com>, Palmer Dabbelt <palmer@dabbelt.com>, Paolo Bonzini <pbonzini@redhat.com>, Paul Walmsley <paul.walmsley@sifive.com>, Shuah Khan <shuah@kernel.org>, virtualization@lists.linux.dev, VMware PV-Drivers Reviewers <pv-drivers@vmware.com>, Will Deacon <will@kernel.org>, x86@kernel.org Subject: Re: [PATCH v5 21/22] KVM: riscv: selftests: Add a test for PMU snapshot functionality Date: Wed, 10 Apr 2024 00:28:08 -0700 [thread overview] Message-ID: <4a428500-4e37-4e7d-968d-3da20dd822af@rivosinc.com> (raw) In-Reply-To: <20240410-2a41e43624596a442d6a95cd@orel> On 4/10/24 00:10, Andrew Jones wrote: > On Tue, Apr 09, 2024 at 03:52:40PM -0700, Atish Patra wrote: >> On 4/5/24 06:11, Andrew Jones wrote: >>> On Wed, Apr 03, 2024 at 01:04:50AM -0700, Atish Patra wrote: > ... >>>> + probe = guest_sbi_probe_extension(SBI_EXT_PMU, &out_val); >>>> + GUEST_ASSERT(probe && out_val == 1); >>>> + >>>> + if (get_host_sbi_spec_version() < sbi_mk_version(2, 0)) >>>> + __GUEST_ASSERT(0, "SBI implementation version doesn't support PMU Snapshot"); >>>> +} >>> It's a pity we can't check the SBI spec version that KVM is advertising >>> from KVM userspace. Normally we'd want to check something like this at >>> the start of the test with TEST_REQUIRE() before running a VCPU in order >>> to generate a skip exit. >>> >> Agreed. I will send a separate series for that as it is an ABI change. >> >>> (We probably should allow reading and even writing the SBI spec version >>> from the VMM in order to better support migration.) >>> >> How that would work for SBI spec version write use case ? For migraiton, you >> can't go back to older SBI versions in the host. Isn't it ? >> >> Considering this case your VM is running with PMU snapshot as the host has >> SBI v2.0. It can't be migrated to v1.0 and expecting it work. Correct ? >> > We can start a VM on a host with SBI v2.0, but tell KVM to tell the VM > that it has v1.0. Then, the guest shouldn't use any features from SBI > that appear after v1.0 and it should be safe to migrate to a host with > v1.0. That depends on when the VMM request to KVM to change the version. Most of SBI implementation checks the SBI version at the boot and enable/disable feature based on the SBI version available. If the SBI version supported by KVM changes to an older one, the calls from VM will fail unexpectedly. > A more likely scenario might be this though: > > 1. KVM userspace checks and captures the SBI version of the host where > the VM is first being launched, e.g. v2.0 > 2. The VM gets migrated to another host which supports something later, > e.g. v3.0, but to > - avoid possibly confusing the guest we tell the destination host > that it should expose v2.0 as the SBI version > - allow rollback to the source host without concern that the guest > has already seen v3.0 and started to use something that the > source can't provide This makes sense though. As per my understanding, we should not allow modifying the SBI version that is less that the version VM already boot with. However, we can allow modifying the SBI version that is higher or same as the VM booted with. I can't think of a use case for the higher version though. > Thanks, > drew
WARNING: multiple messages have this Message-ID (diff)
From: Atish Patra <atishp@rivosinc.com> To: Andrew Jones <ajones@ventanamicro.com> Cc: linux-kernel@vger.kernel.org, Anup Patel <anup@brainfault.org>, Ajay Kaher <akaher@vmware.com>, Alexandre Ghiti <alexghiti@rivosinc.com>, Alexey Makhalov <amakhalov@vmware.com>, Conor Dooley <conor.dooley@microchip.com>, Juergen Gross <jgross@suse.com>, kvm-riscv@lists.infradead.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-riscv@lists.infradead.org, Mark Rutland <mark.rutland@arm.com>, Palmer Dabbelt <palmer@dabbelt.com>, Paolo Bonzini <pbonzini@redhat.com>, Paul Walmsley <paul.walmsley@sifive.com>, Shuah Khan <shuah@kernel.org>, virtualization@lists.linux.dev, VMware PV-Drivers Reviewers <pv-drivers@vmware.com>, Will Deacon <will@kernel.org>, x86@kernel.org Subject: Re: [PATCH v5 21/22] KVM: riscv: selftests: Add a test for PMU snapshot functionality Date: Wed, 10 Apr 2024 00:28:08 -0700 [thread overview] Message-ID: <4a428500-4e37-4e7d-968d-3da20dd822af@rivosinc.com> (raw) In-Reply-To: <20240410-2a41e43624596a442d6a95cd@orel> On 4/10/24 00:10, Andrew Jones wrote: > On Tue, Apr 09, 2024 at 03:52:40PM -0700, Atish Patra wrote: >> On 4/5/24 06:11, Andrew Jones wrote: >>> On Wed, Apr 03, 2024 at 01:04:50AM -0700, Atish Patra wrote: > ... >>>> + probe = guest_sbi_probe_extension(SBI_EXT_PMU, &out_val); >>>> + GUEST_ASSERT(probe && out_val == 1); >>>> + >>>> + if (get_host_sbi_spec_version() < sbi_mk_version(2, 0)) >>>> + __GUEST_ASSERT(0, "SBI implementation version doesn't support PMU Snapshot"); >>>> +} >>> It's a pity we can't check the SBI spec version that KVM is advertising >>> from KVM userspace. Normally we'd want to check something like this at >>> the start of the test with TEST_REQUIRE() before running a VCPU in order >>> to generate a skip exit. >>> >> Agreed. I will send a separate series for that as it is an ABI change. >> >>> (We probably should allow reading and even writing the SBI spec version >>> from the VMM in order to better support migration.) >>> >> How that would work for SBI spec version write use case ? For migraiton, you >> can't go back to older SBI versions in the host. Isn't it ? >> >> Considering this case your VM is running with PMU snapshot as the host has >> SBI v2.0. It can't be migrated to v1.0 and expecting it work. Correct ? >> > We can start a VM on a host with SBI v2.0, but tell KVM to tell the VM > that it has v1.0. Then, the guest shouldn't use any features from SBI > that appear after v1.0 and it should be safe to migrate to a host with > v1.0. That depends on when the VMM request to KVM to change the version. Most of SBI implementation checks the SBI version at the boot and enable/disable feature based on the SBI version available. If the SBI version supported by KVM changes to an older one, the calls from VM will fail unexpectedly. > A more likely scenario might be this though: > > 1. KVM userspace checks and captures the SBI version of the host where > the VM is first being launched, e.g. v2.0 > 2. The VM gets migrated to another host which supports something later, > e.g. v3.0, but to > - avoid possibly confusing the guest we tell the destination host > that it should expose v2.0 as the SBI version > - allow rollback to the source host without concern that the guest > has already seen v3.0 and started to use something that the > source can't provide This makes sense though. As per my understanding, we should not allow modifying the SBI version that is less that the version VM already boot with. However, we can allow modifying the SBI version that is higher or same as the VM booted with. I can't think of a use case for the higher version though. > Thanks, > drew _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv
next prev parent reply other threads:[~2024-04-10 7:28 UTC|newest] Thread overview: 117+ messages / expand[flat|nested] mbox.gz Atom feed top 2024-04-03 8:04 [PATCH v5 00/22] RISC-V SBI v2.0 PMU improvements and Perf sampling in KVM guest Atish Patra 2024-04-03 8:04 ` Atish Patra 2024-04-03 8:04 ` [PATCH v5 01/22] RISC-V: Fix the typo in Scountovf CSR name Atish Patra 2024-04-03 8:04 ` Atish Patra 2024-04-04 10:56 ` Andrew Jones 2024-04-04 10:56 ` Andrew Jones 2024-04-03 8:04 ` [PATCH v5 02/22] RISC-V: Add FIRMWARE_READ_HI definition Atish Patra 2024-04-03 8:04 ` Atish Patra 2024-04-04 10:57 ` Andrew Jones 2024-04-04 10:57 ` Andrew Jones 2024-04-03 8:04 ` [PATCH v5 03/22] drivers/perf: riscv: Read upper bits of a firmware counter Atish Patra 2024-04-03 8:04 ` Atish Patra 2024-04-04 11:02 ` Andrew Jones 2024-04-04 11:02 ` Andrew Jones 2024-04-09 0:04 ` Atish Patra 2024-04-09 0:04 ` Atish Patra 2024-04-03 8:04 ` [PATCH v5 04/22] drivers/perf: riscv: Use BIT macro for shifting operations Atish Patra 2024-04-03 8:04 ` Atish Patra 2024-04-03 15:57 ` unsubscribe jonathan.oleson 2024-04-04 11:08 ` [PATCH v5 04/22] drivers/perf: riscv: Use BIT macro for shifting operations Andrew Jones 2024-04-04 11:08 ` Andrew Jones 2024-04-09 0:20 ` Atish Patra 2024-04-09 0:20 ` Atish Patra 2024-04-03 8:04 ` [PATCH v5 05/22] RISC-V: Add SBI PMU snapshot definitions Atish Patra 2024-04-03 8:04 ` Atish Patra 2024-04-04 11:14 ` Andrew Jones 2024-04-04 11:14 ` Andrew Jones 2024-04-03 8:04 ` [PATCH v5 06/22] drivers/perf: riscv: Implement SBI PMU snapshot function Atish Patra 2024-04-03 8:04 ` Atish Patra 2024-04-04 11:52 ` Andrew Jones 2024-04-04 11:52 ` Andrew Jones 2024-04-10 22:29 ` Atish Patra 2024-04-10 22:29 ` Atish Patra 2024-04-11 7:45 ` Andrew Jones 2024-04-11 7:45 ` Andrew Jones 2024-04-04 12:01 ` Andrew Jones 2024-04-04 12:01 ` Andrew Jones 2024-04-09 0:21 ` Atish Patra 2024-04-09 0:21 ` Atish Patra 2024-04-03 8:04 ` [PATCH v5 07/22] drivers/perf: riscv: Fix counter mask iteration for RV32 Atish Patra 2024-04-03 8:04 ` Atish Patra 2024-04-04 11:55 ` Andrew Jones 2024-04-04 11:55 ` Andrew Jones 2024-04-03 8:04 ` [PATCH v5 08/22] RISC-V: KVM: Fix the initial sample period value Atish Patra 2024-04-03 8:04 ` Atish Patra 2024-04-04 11:57 ` Andrew Jones 2024-04-04 11:57 ` Andrew Jones 2024-04-03 8:04 ` [PATCH v5 09/22] RISC-V: KVM: Rename the SBI_STA_SHMEM_DISABLE to a generic name Atish Patra 2024-04-03 8:04 ` Atish Patra 2024-04-04 11:59 ` Andrew Jones 2024-04-04 11:59 ` Andrew Jones 2024-04-03 8:04 ` [PATCH v5 10/22] RISC-V: KVM: No need to update the counter value during reset Atish Patra 2024-04-03 8:04 ` Atish Patra 2024-04-03 8:04 ` [PATCH v5 11/22] RISC-V: KVM: No need to exit to the user space if perf event failed Atish Patra 2024-04-03 8:04 ` Atish Patra 2024-04-04 12:19 ` Andrew Jones 2024-04-04 12:19 ` Andrew Jones 2024-04-03 8:04 ` [PATCH v5 12/22] RISC-V: KVM: Implement SBI PMU Snapshot feature Atish Patra 2024-04-03 8:04 ` Atish Patra 2024-04-05 11:23 ` Andrew Jones 2024-04-05 11:23 ` Andrew Jones 2024-04-09 0:33 ` Atish Patra 2024-04-09 0:33 ` Atish Patra 2024-04-03 8:04 ` [PATCH v5 13/22] RISC-V: KVM: Add perf sampling support for guests Atish Patra 2024-04-03 8:04 ` Atish Patra 2024-04-05 11:36 ` Andrew Jones 2024-04-05 11:36 ` Andrew Jones 2024-04-03 8:04 ` [PATCH v5 14/22] RISC-V: KVM: Support 64 bit firmware counters on RV32 Atish Patra 2024-04-03 8:04 ` Atish Patra 2024-04-05 12:10 ` Andrew Jones 2024-04-05 12:10 ` Andrew Jones 2024-04-03 8:04 ` [PATCH v5 15/22] RISC-V: KVM: Improve firmware counter read function Atish Patra 2024-04-03 8:04 ` Atish Patra 2024-04-05 12:12 ` Andrew Jones 2024-04-05 12:12 ` Andrew Jones 2024-04-03 8:04 ` [PATCH v5 16/22] KVM: riscv: selftests: Move sbi definitions to its own header file Atish Patra 2024-04-03 8:04 ` Atish Patra 2024-04-05 12:16 ` Andrew Jones 2024-04-05 12:16 ` Andrew Jones 2024-04-03 8:04 ` [PATCH v5 17/22] KVM: riscv: selftests: Add helper functions for extension checks Atish Patra 2024-04-03 8:04 ` Atish Patra 2024-04-05 12:17 ` Andrew Jones 2024-04-05 12:17 ` Andrew Jones 2024-04-03 8:04 ` [PATCH v5 18/22] KVM: riscv: selftests: Add Sscofpmf to get-reg-list test Atish Patra 2024-04-03 8:04 ` Atish Patra 2024-04-03 8:04 ` [PATCH v5 19/22] KVM: riscv: selftests: Add SBI PMU extension definitions Atish Patra 2024-04-03 8:04 ` Atish Patra 2024-04-05 12:20 ` Andrew Jones 2024-04-05 12:20 ` Andrew Jones 2024-04-03 8:04 ` [PATCH v5 20/22] KVM: riscv: selftests: Add SBI PMU selftest Atish Patra 2024-04-03 8:04 ` Atish Patra 2024-04-05 12:50 ` Andrew Jones 2024-04-05 12:50 ` Andrew Jones 2024-04-09 0:37 ` Atish Patra 2024-04-09 0:37 ` Atish Patra 2024-04-09 8:01 ` Andrew Jones 2024-04-09 8:01 ` Andrew Jones 2024-04-09 22:11 ` Atish Kumar Patra 2024-04-09 22:11 ` Atish Kumar Patra 2024-04-03 8:04 ` [PATCH v5 21/22] KVM: riscv: selftests: Add a test for PMU snapshot functionality Atish Patra 2024-04-03 8:04 ` Atish Patra 2024-04-05 13:11 ` Andrew Jones 2024-04-05 13:11 ` Andrew Jones 2024-04-09 22:52 ` Atish Patra 2024-04-09 22:52 ` Atish Patra 2024-04-10 7:10 ` Andrew Jones 2024-04-10 7:10 ` Andrew Jones 2024-04-10 7:28 ` Atish Patra [this message] 2024-04-10 7:28 ` Atish Patra 2024-04-10 7:54 ` Andrew Jones 2024-04-10 7:54 ` Andrew Jones 2024-04-03 8:04 ` [PATCH v5 22/22] KVM: riscv: selftests: Add a test for counter overflow Atish Patra 2024-04-03 8:04 ` Atish Patra 2024-04-05 13:23 ` Andrew Jones 2024-04-05 13:23 ` Andrew Jones 2024-04-09 23:47 ` Atish Patra 2024-04-09 23:47 ` Atish Patra
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