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([38.39.164.180]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-72aad90b302sm1624733b3a.175.2024.12.19.10.32.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Dec 2024 10:32:14 -0800 (PST) From: Pierrick Bouvier To: qemu-devel@nongnu.org Cc: Eduardo Habkost , Fabiano Rosas , Peter Maydell , Yanan Wang , Zhao Liu , qemu-arm@nongnu.org, Laurent Vivier , alex.bennee@linaro.org, =?utf-8?q?Philippe_Mathieu-Daud=C3=A9?= , Paolo Bonzini , Marcel Apfelbaum , Pierrick Bouvier Subject: [PATCH v2 1/3] target/arm: add new property to select pauth-qarma5 Date: Thu, 19 Dec 2024 10:32:09 -0800 Message-Id: <20241219183211.3493974-2-pierrick.bouvier@linaro.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20241219183211.3493974-1-pierrick.bouvier@linaro.org> References: <20241219183211.3493974-1-pierrick.bouvier@linaro.org> MIME-Version: 1.0 Received-SPF: pass client-ip=2607:f8b0:4864:20::42b; envelope-from=pierrick.bouvier@linaro.org; helo=mail-pf1-x42b.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+patch=linaro.org@nongnu.org Sender: qemu-devel-bounces+patch=linaro.org@nongnu.org Before changing default pauth algorithm, we need to make sure current default one (QARMA5) can still be selected. $ qemu-system-aarch64 -cpu max,pauth-qarma5=on ... Signed-off-by: Pierrick Bouvier Reviewed-by: Richard Henderson --- docs/system/arm/cpu-features.rst | 5 ++++- target/arm/cpu.h | 1 + target/arm/arm-qmp-cmds.c | 2 +- target/arm/cpu64.c | 20 ++++++++++++++------ tests/qtest/arm-cpu-features.c | 15 +++++++++++---- 5 files changed, 31 insertions(+), 12 deletions(-) diff --git a/docs/system/arm/cpu-features.rst b/docs/system/arm/cpu-features.rst index a5fb929243c..d69ebc2b852 100644 --- a/docs/system/arm/cpu-features.rst +++ b/docs/system/arm/cpu-features.rst @@ -219,7 +219,10 @@ Below is the list of TCG VCPU features and their descriptions. ``pauth-qarma3`` When ``pauth`` is enabled, select the architected QARMA3 algorithm. -Without either ``pauth-impdef`` or ``pauth-qarma3`` enabled, +``pauth-qarma5`` + When ``pauth`` is enabled, select the architected QARMA5 algorithm. + +Without ``pauth-impdef``, ``pauth-qarma3`` or ``pauth-qarma5`` enabled, the architected QARMA5 algorithm is used. The architected QARMA5 and QARMA3 algorithms have good cryptographic properties, but can be quite slow to emulate. The impdef algorithm used by QEMU is diff --git a/target/arm/cpu.h b/target/arm/cpu.h index d86e641280d..b7500bebd7f 100644 --- a/target/arm/cpu.h +++ b/target/arm/cpu.h @@ -1062,6 +1062,7 @@ struct ArchCPU { bool prop_pauth; bool prop_pauth_impdef; bool prop_pauth_qarma3; + bool prop_pauth_qarma5; bool prop_lpa2; /* DCZ blocksize, in log_2(words), ie low 4 bits of DCZID_EL0 */ diff --git a/target/arm/arm-qmp-cmds.c b/target/arm/arm-qmp-cmds.c index 3cc8cc738bb..33cea080d11 100644 --- a/target/arm/arm-qmp-cmds.c +++ b/target/arm/arm-qmp-cmds.c @@ -94,7 +94,7 @@ static const char *cpu_model_advertised_features[] = { "sve640", "sve768", "sve896", "sve1024", "sve1152", "sve1280", "sve1408", "sve1536", "sve1664", "sve1792", "sve1920", "sve2048", "kvm-no-adjvtime", "kvm-steal-time", - "pauth", "pauth-impdef", "pauth-qarma3", + "pauth", "pauth-impdef", "pauth-qarma3", "pauth-qarma5", NULL }; diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c index ec77c5b34ad..9a193d2b489 100644 --- a/target/arm/cpu64.c +++ b/target/arm/cpu64.c @@ -520,9 +520,12 @@ void arm_cpu_pauth_finalize(ARMCPU *cpu, Error **errp) } if (cpu->prop_pauth) { - if (cpu->prop_pauth_impdef && cpu->prop_pauth_qarma3) { + if ((cpu->prop_pauth_impdef && cpu->prop_pauth_qarma3) || + (cpu->prop_pauth_impdef && cpu->prop_pauth_qarma5) || + (cpu->prop_pauth_qarma3 && cpu->prop_pauth_qarma5)) { error_setg(errp, - "cannot enable both pauth-impdef and pauth-qarma3"); + "cannot enable pauth-impdef, pauth-qarma3 and " + "pauth-qarma5 at the same time"); return; } @@ -532,13 +535,15 @@ void arm_cpu_pauth_finalize(ARMCPU *cpu, Error **errp) } else if (cpu->prop_pauth_qarma3) { isar2 = FIELD_DP64(isar2, ID_AA64ISAR2, APA3, features); isar2 = FIELD_DP64(isar2, ID_AA64ISAR2, GPA3, 1); - } else { + } else { /* default is pauth-qarma5 */ isar1 = FIELD_DP64(isar1, ID_AA64ISAR1, APA, features); isar1 = FIELD_DP64(isar1, ID_AA64ISAR1, GPA, 1); } - } else if (cpu->prop_pauth_impdef || cpu->prop_pauth_qarma3) { - error_setg(errp, "cannot enable pauth-impdef or " - "pauth-qarma3 without pauth"); + } else if (cpu->prop_pauth_impdef || + cpu->prop_pauth_qarma3 || + cpu->prop_pauth_qarma5) { + error_setg(errp, "cannot enable pauth-impdef, pauth-qarma3 or " + "pauth-qarma5 without pauth"); error_append_hint(errp, "Add pauth=on to the CPU property list.\n"); } } @@ -553,6 +558,8 @@ static const Property arm_cpu_pauth_impdef_property = DEFINE_PROP_BOOL("pauth-impdef", ARMCPU, prop_pauth_impdef, false); static const Property arm_cpu_pauth_qarma3_property = DEFINE_PROP_BOOL("pauth-qarma3", ARMCPU, prop_pauth_qarma3, false); +static Property arm_cpu_pauth_qarma5_property = + DEFINE_PROP_BOOL("pauth-qarma5", ARMCPU, prop_pauth_qarma5, false); void aarch64_add_pauth_properties(Object *obj) { @@ -573,6 +580,7 @@ void aarch64_add_pauth_properties(Object *obj) } else { qdev_property_add_static(DEVICE(obj), &arm_cpu_pauth_impdef_property); qdev_property_add_static(DEVICE(obj), &arm_cpu_pauth_qarma3_property); + qdev_property_add_static(DEVICE(obj), &arm_cpu_pauth_qarma5_property); } } diff --git a/tests/qtest/arm-cpu-features.c b/tests/qtest/arm-cpu-features.c index cfd6f773535..98d6c970ea5 100644 --- a/tests/qtest/arm-cpu-features.c +++ b/tests/qtest/arm-cpu-features.c @@ -419,21 +419,28 @@ static void pauth_tests_default(QTestState *qts, const char *cpu_type) assert_has_feature_enabled(qts, cpu_type, "pauth"); assert_has_feature_disabled(qts, cpu_type, "pauth-impdef"); assert_has_feature_disabled(qts, cpu_type, "pauth-qarma3"); + assert_has_feature_disabled(qts, cpu_type, "pauth-qarma5"); assert_set_feature(qts, cpu_type, "pauth", false); assert_set_feature(qts, cpu_type, "pauth", true); assert_set_feature(qts, cpu_type, "pauth-impdef", true); assert_set_feature(qts, cpu_type, "pauth-impdef", false); assert_set_feature(qts, cpu_type, "pauth-qarma3", true); assert_set_feature(qts, cpu_type, "pauth-qarma3", false); + assert_set_feature(qts, cpu_type, "pauth-qarma5", true); + assert_set_feature(qts, cpu_type, "pauth-qarma5", false); assert_error(qts, cpu_type, - "cannot enable pauth-impdef or pauth-qarma3 without pauth", + "cannot enable pauth-impdef, pauth-qarma3 or pauth-qarma5 without pauth", "{ 'pauth': false, 'pauth-impdef': true }"); assert_error(qts, cpu_type, - "cannot enable pauth-impdef or pauth-qarma3 without pauth", + "cannot enable pauth-impdef, pauth-qarma3 or pauth-qarma5 without pauth", "{ 'pauth': false, 'pauth-qarma3': true }"); assert_error(qts, cpu_type, - "cannot enable both pauth-impdef and pauth-qarma3", - "{ 'pauth': true, 'pauth-impdef': true, 'pauth-qarma3': true }"); + "cannot enable pauth-impdef, pauth-qarma3 or pauth-qarma5 without pauth", + "{ 'pauth': false, 'pauth-qarma5': true }"); + assert_error(qts, cpu_type, + "cannot enable pauth-impdef, pauth-qarma3 and pauth-qarma5 at the same time", + "{ 'pauth': true, 'pauth-impdef': true, 'pauth-qarma3': true," + " 'pauth-qarma5': true }"); } static void test_query_cpu_model_expansion(const void *data) From patchwork Thu Dec 19 18:32:10 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Pierrick Bouvier X-Patchwork-Id: 852043 Delivered-To: patch@linaro.org Received: by 2002:a5d:4888:0:b0:385:e875:8a9e with SMTP id g8csp1650199wrq; Thu, 19 Dec 2024 10:33:27 -0800 (PST) X-Forwarded-Encrypted: i=2; AJvYcCVxmmjWPoruJlHk2gWpslVtlIJVceqEp/c4rcCAt3V+HpzRMGHPTgI4Jn3fO5aE1h/FHmgG/A==@linaro.org X-Google-Smtp-Source: AGHT+IHAIBA6B+yWvHEoFTQLBPp/wk/nhlD9PqJd2NzVnpGTAzRjm3fzdQ14A9/b+/oz0Qk7g29P X-Received: by 2002:a05:6122:2105:b0:516:1e32:f8c7 with SMTP id 71dfb90a1353d-51b6496ebd5mr5264083e0c.0.1734633207051; 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([38.39.164.180]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-72aad90b302sm1624733b3a.175.2024.12.19.10.32.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Dec 2024 10:32:15 -0800 (PST) From: Pierrick Bouvier To: qemu-devel@nongnu.org Cc: Eduardo Habkost , Fabiano Rosas , Peter Maydell , Yanan Wang , Zhao Liu , qemu-arm@nongnu.org, Laurent Vivier , alex.bennee@linaro.org, =?utf-8?q?Philippe_Mathieu-Daud=C3=A9?= , Paolo Bonzini , Marcel Apfelbaum , Pierrick Bouvier Subject: [PATCH v2 2/3] target/arm: change default pauth algorithm to impdef Date: Thu, 19 Dec 2024 10:32:10 -0800 Message-Id: <20241219183211.3493974-3-pierrick.bouvier@linaro.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20241219183211.3493974-1-pierrick.bouvier@linaro.org> References: <20241219183211.3493974-1-pierrick.bouvier@linaro.org> MIME-Version: 1.0 Received-SPF: pass client-ip=2607:f8b0:4864:20::432; envelope-from=pierrick.bouvier@linaro.org; helo=mail-pf1-x432.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+patch=linaro.org@nongnu.org Sender: qemu-devel-bounces+patch=linaro.org@nongnu.org Pointer authentication on aarch64 is pretty expensive (up to 50% of execution time) when running a virtual machine with tcg and -cpu max (which enables pauth=on). The advice is always: use pauth-impdef=on. Our documentation even mentions it "by default" in docs/system/introduction.rst. Thus, we change the default to use impdef by default. This does not affect kvm or hvf acceleration, since pauth algorithm used is the one from host cpu. This change is retro compatible, in terms of cli, with previous versions, as the semantic of using -cpu max,pauth-impdef=on, and -cpu max,pauth-qarma3=on is preserved. The new option introduced in previous patch and matching old default is -cpu max,pauth-qarma5=on. It is retro compatible with migration as well, by defining a backcompat property, that will use qarma5 by default for virt machine <= 9.2. Tested by saving and restoring a vm from qemu 9.2.0 into qemu-master (10.0) for cpus neoverse-n2 and max. Signed-off-by: Pierrick Bouvier Reviewed-by: Richard Henderson --- docs/system/arm/cpu-features.rst | 2 +- docs/system/introduction.rst | 2 +- target/arm/cpu.h | 3 +++ hw/core/machine.c | 4 +++- target/arm/cpu.c | 2 ++ target/arm/cpu64.c | 22 ++++++++++++++++------ 6 files changed, 26 insertions(+), 9 deletions(-) diff --git a/docs/system/arm/cpu-features.rst b/docs/system/arm/cpu-features.rst index d69ebc2b852..37d5dfd15b3 100644 --- a/docs/system/arm/cpu-features.rst +++ b/docs/system/arm/cpu-features.rst @@ -223,7 +223,7 @@ Below is the list of TCG VCPU features and their descriptions. When ``pauth`` is enabled, select the architected QARMA5 algorithm. Without ``pauth-impdef``, ``pauth-qarma3`` or ``pauth-qarma5`` enabled, -the architected QARMA5 algorithm is used. The architected QARMA5 +the QEMU impdef algorithm is used. The architected QARMA5 and QARMA3 algorithms have good cryptographic properties, but can be quite slow to emulate. The impdef algorithm used by QEMU is non-cryptographic but significantly faster. diff --git a/docs/system/introduction.rst b/docs/system/introduction.rst index 746707eb00e..338d3745c3c 100644 --- a/docs/system/introduction.rst +++ b/docs/system/introduction.rst @@ -169,7 +169,7 @@ would default to it anyway. .. code:: - -cpu max,pauth-impdef=on \ + -cpu max \ -smp 4 \ -accel tcg \ diff --git a/target/arm/cpu.h b/target/arm/cpu.h index b7500bebd7f..276a7a557ba 100644 --- a/target/arm/cpu.h +++ b/target/arm/cpu.h @@ -972,6 +972,9 @@ struct ArchCPU { /* QOM property to indicate we should use the back-compat CNTFRQ default */ bool backcompat_cntfrq; + /* QOM property to indicate we should use the back-compat QARMA5 default */ + bool backcompat_pauth_default_use_qarma5; + /* Specify the number of cores in this CPU cluster. Used for the L2CTLR * register. */ diff --git a/hw/core/machine.c b/hw/core/machine.c index d970f753e37..de1547994c4 100644 --- a/hw/core/machine.c +++ b/hw/core/machine.c @@ -36,7 +36,9 @@ #include "hw/virtio/virtio-iommu.h" #include "audio/audio.h" -GlobalProperty hw_compat_9_2[] = {}; +GlobalProperty hw_compat_9_2[] = { + {"arm-cpu", "backcompat-pauth-default-use-qarma5", "true"}, +}; const size_t hw_compat_9_2_len = G_N_ELEMENTS(hw_compat_9_2); GlobalProperty hw_compat_9_1[] = { diff --git a/target/arm/cpu.c b/target/arm/cpu.c index 1afa07511e3..68f1ab639b8 100644 --- a/target/arm/cpu.c +++ b/target/arm/cpu.c @@ -2652,6 +2652,8 @@ static const Property arm_cpu_properties[] = { DEFINE_PROP_INT32("core-count", ARMCPU, core_count, -1), /* True to default to the backward-compat old CNTFRQ rather than 1Ghz */ DEFINE_PROP_BOOL("backcompat-cntfrq", ARMCPU, backcompat_cntfrq, false), + DEFINE_PROP_BOOL("backcompat-pauth-default-use-qarma5", ARMCPU, + backcompat_pauth_default_use_qarma5, false), DEFINE_PROP_END_OF_LIST() }; diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c index 9a193d2b489..045b94fcb4d 100644 --- a/target/arm/cpu64.c +++ b/target/arm/cpu64.c @@ -529,15 +529,25 @@ void arm_cpu_pauth_finalize(ARMCPU *cpu, Error **errp) return; } - if (cpu->prop_pauth_impdef) { - isar1 = FIELD_DP64(isar1, ID_AA64ISAR1, API, features); - isar1 = FIELD_DP64(isar1, ID_AA64ISAR1, GPI, 1); + bool use_default = !cpu->prop_pauth_qarma5 && + !cpu->prop_pauth_qarma3 && + !cpu->prop_pauth_impdef; + + if (cpu->prop_pauth_qarma5 || + (use_default && + cpu->backcompat_pauth_default_use_qarma5)) { + isar1 = FIELD_DP64(isar1, ID_AA64ISAR1, APA, features); + isar1 = FIELD_DP64(isar1, ID_AA64ISAR1, GPA, 1); } else if (cpu->prop_pauth_qarma3) { isar2 = FIELD_DP64(isar2, ID_AA64ISAR2, APA3, features); isar2 = FIELD_DP64(isar2, ID_AA64ISAR2, GPA3, 1); - } else { /* default is pauth-qarma5 */ - isar1 = FIELD_DP64(isar1, ID_AA64ISAR1, APA, features); - isar1 = FIELD_DP64(isar1, ID_AA64ISAR1, GPA, 1); + } else if (cpu->prop_pauth_impdef || + (use_default && + !cpu->backcompat_pauth_default_use_qarma5)) { + isar1 = FIELD_DP64(isar1, ID_AA64ISAR1, API, features); + isar1 = FIELD_DP64(isar1, ID_AA64ISAR1, GPI, 1); + } else { + g_assert_not_reached(); } } else if (cpu->prop_pauth_impdef || cpu->prop_pauth_qarma3 || From patchwork Thu Dec 19 18:32:11 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Pierrick Bouvier X-Patchwork-Id: 852046 Delivered-To: patch@linaro.org Received: by 2002:a5d:4888:0:b0:385:e875:8a9e with SMTP id g8csp1650213wrq; Thu, 19 Dec 2024 10:33:28 -0800 (PST) X-Forwarded-Encrypted: i=2; AJvYcCVIVhiC5QhvP5uLIh7lj+/oEThPeZDQujkcnuyaO25u76QvELmA97eHamWEFVs40DKdOerOQw==@linaro.org X-Google-Smtp-Source: AGHT+IF8sKxIq0PcV6WHPFgNxVs6sVbAylACwYGeL35+SHHH8y8BJ30nVeLYTEJTFwHkrQZTBKql X-Received: by 2002:a05:6214:2387:b0:6d8:a7e1:e270 with SMTP id 6a1803df08f44-6dd21f77022mr7265436d6.40.1734633208472; Thu, 19 Dec 2024 10:33:28 -0800 (PST) ARC-Seal: i=1; a=rsa-sha256; t=1734633208; cv=none; d=google.com; s=arc-20240605; b=gl9I2OPx/XTIOwlE/iNjn9ElvfeArZXF5Hn+nF2v1K0auks1j2773f3NZ8/wyEtNsH EKul+dgKwi9GOImxsxR9FylP86MKUfowMR/b0SP1kFS1kJ16Z09bHMuEnTSK1+IpG2DH 2xPkLmI60qJWARf7KMxpwvDsNgrYx+2TRYfg+BaLawcYpZB3NXFLHeXlaZUZiVj/LKvk Gy2UunFKgWa2/oV/dXqqgSb2jfsRMu2qoF4JMtjulMsYWosb1+WUVfJAfzLE/805BmOS SxlmoKZKwPk90Lg162+HN8tVY+DMdSbgNShJf6I6lAR5W8sHMhVsucU5cGhtEl4Q4xNF KTnA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20240605; h=sender:errors-to:list-subscribe:list-help:list-post:list-archive :list-unsubscribe:list-id:precedence:content-transfer-encoding :mime-version:references:in-reply-to:message-id:date:subject:cc:to :from:dkim-signature; bh=VrAuDbFs90HcBriKC3fRwSGZ9LUrKAcdlzz9HBsoE2g=; fh=15DwK79D2poCFMOXmyE/Rt20KtPvvEZtK1Roylr48Rs=; b=ULVBs5S0cAg5eu5YsGqiOTPIpzzCezTaxz7m9j316KwlqFbkWLNg/8wLFhq2Z972We LCgBwbQC9cfN8HCej/Xtn+ndZXlAykT1Zp8MvM7tWpVC4cmEGI9ZHtg7DXWzEWLcBTsh pJtDkZYY5INX1BpLDICSPvQJpqhulE2GecYQ2ASIIYJfV3vt2wYoP+MIIA//njFvCTe7 0MTYzoXWuPkAVudX+A0hbpjkq5RzcjAGrYuTQ9A8kMCO6P1WikysE48gQd1yvhAEIZl+ bd/Ks39FCvseQuVzKoK6/Wh7VEcf2WKT6CzJzTVUvEkwmdi/Q9bp6WXPx2LQn8/Gqa2k heuQ==; dara=google.com ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@linaro.org header.s=google header.b=TBD4mrez; spf=pass (google.com: domain of qemu-devel-bounces+patch=linaro.org@nongnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom="qemu-devel-bounces+patch=linaro.org@nongnu.org"; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=linaro.org; dara=neutral header.i=@linaro.org Return-Path: Received: from lists.gnu.org (lists.gnu.org. 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([38.39.164.180]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-72aad90b302sm1624733b3a.175.2024.12.19.10.32.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Dec 2024 10:32:16 -0800 (PST) From: Pierrick Bouvier To: qemu-devel@nongnu.org Cc: Eduardo Habkost , Fabiano Rosas , Peter Maydell , Yanan Wang , Zhao Liu , qemu-arm@nongnu.org, Laurent Vivier , alex.bennee@linaro.org, =?utf-8?q?Philippe_Mathieu-Daud=C3=A9?= , Paolo Bonzini , Marcel Apfelbaum , Pierrick Bouvier Subject: [PATCH v2 3/3] docs/system/arm/virt: mention specific migration information Date: Thu, 19 Dec 2024 10:32:11 -0800 Message-Id: <20241219183211.3493974-4-pierrick.bouvier@linaro.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20241219183211.3493974-1-pierrick.bouvier@linaro.org> References: <20241219183211.3493974-1-pierrick.bouvier@linaro.org> MIME-Version: 1.0 Received-SPF: pass client-ip=2607:f8b0:4864:20::42e; envelope-from=pierrick.bouvier@linaro.org; helo=mail-pf1-x42e.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, WEIRD_QUOTING=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+patch=linaro.org@nongnu.org Sender: qemu-devel-bounces+patch=linaro.org@nongnu.org Signed-off-by: Pierrick Bouvier --- docs/system/arm/virt.rst | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst index d25275c27ce..9f1457cf9a2 100644 --- a/docs/system/arm/virt.rst +++ b/docs/system/arm/virt.rst @@ -17,9 +17,17 @@ to have the same behaviour as that of previous QEMU releases, so that VM migration will work between QEMU versions. For instance the ``virt-5.0`` machine type will behave like the ``virt`` machine from the QEMU 5.0 release, and migration should work between ``virt-5.0`` -of the 5.0 release and ``virt-5.0`` of the 5.1 release. Migration -is not guaranteed to work between different QEMU releases for -the non-versioned ``virt`` machine type. +of the 5.0 release and ``virt-5.0`` of the 5.1 release. + +When saving a VM using the ``virt`` model, the snapshot is automatically set to +target the latest ``virt`` versioned model. When loading the VM with a more +recent QEMU version, you'll need to set machine model to match the version of +your snapshot. When loading it, QEMU will return an error with the expected +``virt`` version you should set, so you don't need to record it. + +VM migration is not guaranteed when using ``-cpu max``, as features supported +may change between QEMU versions. To ensure your VM can be migrated, it is +recommended to use another cpu model instead. Supported devices """""""""""""""""