From nobody Fri Nov 14 15:22:08 2025 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=git.sr.ht Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1762381959271894.5192136745654; Wed, 5 Nov 2025 14:32:39 -0800 (PST) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vGm2n-00022H-Vs; Wed, 05 Nov 2025 17:31:58 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1vGm2h-00021O-PT for qemu-devel@nongnu.org; Wed, 05 Nov 2025 17:31:54 -0500 Received: from mail-a.sr.ht ([46.23.81.152]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1vGm2e-0007UN-Fm for qemu-devel@nongnu.org; Wed, 05 Nov 2025 17:31:50 -0500 Received: from git.sr.ht (unknown [46.23.81.155]) by mail-a.sr.ht (Postfix) with ESMTPSA id B0EB8240C3; Wed, 05 Nov 2025 22:31:44 +0000 (UTC) DKIM-Signature: a=rsa-sha256; bh=rN5skFE/7t7CivcRFcehEgzgv/YQF41xi+DFhFMhlZc=; c=simple/simple; d=git.sr.ht; h=From:Date:Subject:Reply-to:In-Reply-To:To:Cc; q=dns/txt; s=20240113; t=1762381904; v=1; b=XyYfe42HVuq5sHS6ubQVWZKbis8/IPnIm36tTXBdvZemuS+Gtcqn7TWv0qL3GHOmnc0eCd3C pZDEPsGKtnzPIPmC+CWXYfulVQi1GvHxBX/iTX7VBQmbj9808KTI+qAIfkySnCKvsoZCBBgEH9u 8h3+i2GzbTvQir7zT87dS1Ajmj0T6mHzy4joRzrSpQU7aXadPBjVN4eXDoa3idEwpcvk1DpWCNa uiCwI5eYJyh+/2dnMPF/zzZpt7a6/3v/3nf//GU4VUGUV2xgenbhSsi6cQujH5BIfYoXjLYrubq syGk5sA0Ui2TW07Rqs93EOG+teGbZ/wuH53gj8m1Sxxsw== From: ~myrslint Date: Wed, 05 Nov 2025 22:07:10 +0000 Subject: [PATCH qemu v9 1/1] i386/kvm: Honor guest PAT on x86, absent Bochs display Message-ID: <176238190422.23756.12141073071212582632-1@git.sr.ht> X-Mailer: git.sr.ht In-Reply-To: <176238190422.23756.12141073071212582632-0@git.sr.ht> To: qemu-devel@nongnu.org Cc: Dmitry Osipenko , Paolo Bonzini , Gerd Hoffmann Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=46.23.81.152; envelope-from=outgoing@sr.ht; helo=mail-a.sr.ht X-Spam_score_int: -16 X-Spam_score: -1.7 X-Spam_bar: - X-Spam_report: (-1.7 / 5.0 requ) BAYES_00=-1.9, DKIM_INVALID=0.1, DKIM_SIGNED=0.1, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=no 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: , Reply-To: ~myrslint Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZM-MESSAGEID: 1762381963535154100 From: myrslint On x86_64, where most CPUs support self-snoop, it is preferrable to always honor guest PAT. Not doing so is a quirk. There is a default enabled KVM quirk flag which enforces not doing so due to a former bug in Bochs display driver. The bug has been fixed but not enough has yet passed since so we only disable said quirk flag if a Bochs display is not configured for the virtual machine. This commit also moves around a bit of code that would be called when the initialization of a VM is done. Signed-off-by: Myrsky Lintu Reviewed-by: Dmitry Osipenko Tested-by: Dmitry Osipenko # intel-ivb --- accel/kvm/kvm-all.c | 1 + accel/stubs/kvm-stub.c | 1 + hw/display/bochs-display.c | 17 +++++++++++++++ include/system/kvm.h | 9 ++++++++ target/i386/kvm/kvm.c | 42 +++++++++++++++++++++++++++++++------- 5 files changed, 63 insertions(+), 7 deletions(-) diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c index f9254ae654..36a12593ee 100644 --- a/accel/kvm/kvm-all.c +++ b/accel/kvm/kvm-all.c @@ -103,6 +103,7 @@ bool kvm_readonly_mem_allowed; bool kvm_vm_attributes_allowed; bool kvm_msi_use_devid; bool kvm_pre_fault_memory_supported; +bool kvm_bochs_drm_quirk; static bool kvm_has_guest_debug; static int kvm_sstep_flags; static bool kvm_immediate_exit; diff --git a/accel/stubs/kvm-stub.c b/accel/stubs/kvm-stub.c index 68cd33ba97..a69c89e1ad 100644 --- a/accel/stubs/kvm-stub.c +++ b/accel/stubs/kvm-stub.c @@ -24,6 +24,7 @@ bool kvm_gsi_direct_mapping; bool kvm_allowed; bool kvm_readonly_mem_allowed; bool kvm_msi_use_devid; +bool kvm_bochs_drm_quirk; =20 void kvm_flush_coalesced_mmio_buffer(void) { diff --git a/hw/display/bochs-display.c b/hw/display/bochs-display.c index ad2821c974..e8def68b41 100644 --- a/hw/display/bochs-display.c +++ b/hw/display/bochs-display.c @@ -20,6 +20,8 @@ #include "ui/qemu-pixman.h" #include "qom/object.h" =20 +#include "system/kvm.h" + typedef struct BochsDisplayMode { pixman_format_code_t format; uint32_t bytepp; @@ -309,6 +311,21 @@ static void bochs_display_realize(PCIDevice *dev, Erro= r **errp) } =20 memory_region_set_log(&s->vram, true, DIRTY_MEMORY_VGA); + + /* + * On x86_64, where most CPUs support self-snoop, it is preferrable to + * always honor guest PAT. Not doing so is a quirk. There is a default + * enabled KVM quirk flag which enforces not doing so due to a former = bug + * in Bochs display driver. + * + * The bug has been fixed but not enough has yet passed since so we on= ly + * disable said quirk flag if a Bochs display is not configured for the + * virtual machine. + * + * The following flag tells KVM initialization code not to disable that + * quirk flag. + */ + kvm_bochs_drm_quirk =3D true; } =20 static bool bochs_display_get_big_endian_fb(Object *obj, Error **errp) diff --git a/include/system/kvm.h b/include/system/kvm.h index 8f9eecf044..123016777c 100644 --- a/include/system/kvm.h +++ b/include/system/kvm.h @@ -43,6 +43,7 @@ extern bool kvm_gsi_direct_mapping; extern bool kvm_readonly_mem_allowed; extern bool kvm_msi_use_devid; extern bool kvm_pre_fault_memory_supported; +extern bool kvm_bochs_drm_quirk; =20 #define kvm_enabled() (kvm_allowed) /** @@ -144,6 +145,13 @@ extern bool kvm_pre_fault_memory_supported; */ #define kvm_msi_devid_required() (kvm_msi_use_devid) =20 +/** + * kvm_has_bochs_drm: + * Returns: true if KVM is possible and a Bochs DRM driver is + * in use for display. + */ +#define kvm_has_bochs_drm() (kvm_bochs_drm_quirk) + #else =20 #define kvm_enabled() (0) @@ -158,6 +166,7 @@ extern bool kvm_pre_fault_memory_supported; #define kvm_gsi_direct_mapping() (false) #define kvm_readonly_mem_enabled() (false) #define kvm_msi_devid_required() (false) +#define kvm_has_bochs_drm() (false) =20 #endif /* CONFIG_KVM_IS_POSSIBLE */ =20 diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c index 60c7981138..dd2594f5af 100644 --- a/target/i386/kvm/kvm.c +++ b/target/i386/kvm/kvm.c @@ -2709,13 +2709,13 @@ static bool kvm_rdmsr_pkg_energy_status(X86CPU *cpu, return true; } =20 -static Notifier smram_machine_done; +static Notifier kvm_machine_done; static KVMMemoryListener smram_listener; static AddressSpace smram_address_space; static MemoryRegion smram_as_root; static MemoryRegion smram_as_mem; =20 -static void register_smram_listener(Notifier *n, void *unused) +static void register_smram_listener(void) { CPUState *cpu; MemoryRegion *smram =3D @@ -2754,6 +2754,37 @@ void kvm_smm_cpu_address_space_init(X86CPU *cpu) cpu_address_space_init(CPU(cpu), X86ASIdx_SMM, "cpu-smm", &smram_as_ro= ot); } =20 +static bool kvm_x86_smm_enabled(void) +{ + return object_dynamic_cast(OBJECT(current_machine), TYPE_X86_MACHINE) = && + x86_machine_is_smm_enabled(X86_MACHINE(current_machine)); +} + +static int kvm_x86_disable_quirsk2_mask(void) +{ + return kvm_check_extension(kvm_state, KVM_CAP_DISABLE_QUIRKS2); +} + +static int kvm_disable_ignore_guest_pat(void) +{ + return kvm_vm_enable_cap(kvm_state, KVM_CAP_DISABLE_QUIRKS2, 0, \ + KVM_X86_QUIRK_IGNORE_GUEST_PAT); +} + +static void handle_machine_done(Notifier *n, void *unused) +{ + if (kvm_x86_smm_enabled()) { + register_smram_listener(); + } + if (!kvm_has_bochs_drm() && \ + (kvm_x86_disable_quirsk2_mask() & KVM_X86_QUIRK_IGNORE_GUEST_PAT))= { + if (kvm_disable_ignore_guest_pat()) { + error_report("KVM_X86_QUIRK_IGNORE_GUEST_PAT available and " + "modifiable but we failed to disable it"); + } + } +} + static void *kvm_msr_energy_thread(void *data) { KVMState *s =3D data; @@ -3334,11 +3365,8 @@ int kvm_arch_init(MachineState *ms, KVMState *s) return ret; } =20 - if (object_dynamic_cast(OBJECT(ms), TYPE_X86_MACHINE) && - x86_machine_is_smm_enabled(X86_MACHINE(ms))) { - smram_machine_done.notify =3D register_smram_listener; - qemu_add_machine_init_done_notifier(&smram_machine_done); - } + kvm_machine_done.notify =3D handle_machine_done; + qemu_add_machine_init_done_notifier(&kvm_machine_done); =20 if (enable_cpu_pm) { ret =3D kvm_vm_enable_disable_exits(s); --=20 2.49.1