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Thu, 22 Jul 2021 05:53:17 +0000 From: Michael Kelley To: Praveen Kumar , "linux-hyperv@vger.kernel.org" , "linux-kernel@vger.kernel.org" CC: KY Srinivasan , Haiyang Zhang , Stephen Hemminger , "wei.liu@kernel.org" , Dexuan Cui , "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "x86@kernel.org" , "hpa@zytor.com" , "viremana@linux.microsoft.com" , Sunil Muthuswamy , "nunodasneves@linux.microsoft.com" Subject: RE: [PATCH v2] hyperv: root partition faults writing to VP ASSIST MSR PAGE Thread-Topic: [PATCH v2] hyperv: root partition faults writing to VP ASSIST MSR PAGE Thread-Index: AQHXflrRy8cubGTIiUy0u2ResSeyhatOejGA Date: Thu, 22 Jul 2021 05:53:17 +0000 Message-ID: References: <20210721180302.18764-1-kumarpraveen@linux.microsoft.com> In-Reply-To: <20210721180302.18764-1-kumarpraveen@linux.microsoft.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: msip_labels: MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_ActionId=086bd09e-5d1c-4898-a9a3-d3910ada4740;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_ContentBits=0;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Enabled=true;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Method=Standard;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Name=Internal;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_SetDate=2021-07-22T05:35:59Z;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_SiteId=72f988bf-86f1-41af-91ab-2d7cd011db47; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: microsoft.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: MWHPR21MB1593.namprd21.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 5f88e74b-f56d-467a-6b9a-08d94cd500ba X-MS-Exchange-CrossTenant-originalarrivaltime: 22 Jul 2021 05:53:17.2208 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: lxqCiKfnkfOB94e3Us3TEXT3FLejFvDb4iwYvrGZIrGdPm9wzcbo7LsRXQKprAPrw0RLoUQw5NWaleAPS5OTE5pofVnJpOnvSYdjrqcx4nw= X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW4PR21MB2025 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Praveen Kumar Sent: Wednesday, Jul= y 21, 2021 11:03 AM >=20 > For Root partition the VP assist pages are pre-determined by the > hypervisor. The Root kernel is not allowed to change them to > different locations. And thus, we are getting below stack as in > current implementation Root is trying to perform write to specific > MSR. >=20 > [ 2.778197] unchecked MSR access error: WRMSR to 0x40000073 (tried to > write 0x0000000145ac5001) at rIP: 0xffffffff810c1084 > (native_write_msr+0x4/0x30) > [ 2.784867] Call Trace: > [ 2.791507] hv_cpu_init+0xf1/0x1c0 > [ 2.798144] ? hyperv_report_panic+0xd0/0xd0 > [ 2.804806] cpuhp_invoke_callback+0x11a/0x440 > [ 2.811465] ? hv_resume+0x90/0x90 > [ 2.818137] cpuhp_issue_call+0x126/0x130 > [ 2.824782] __cpuhp_setup_state_cpuslocked+0x102/0x2b0 > [ 2.831427] ? hyperv_report_panic+0xd0/0xd0 > [ 2.838075] ? hyperv_report_panic+0xd0/0xd0 > [ 2.844723] ? hv_resume+0x90/0x90 > [ 2.851375] __cpuhp_setup_state+0x3d/0x90 > [ 2.858030] hyperv_init+0x14e/0x410 > [ 2.864689] ? enable_IR_x2apic+0x190/0x1a0 > [ 2.871349] apic_intr_mode_init+0x8b/0x100 > [ 2.878017] x86_late_time_init+0x20/0x30 > [ 2.884675] start_kernel+0x459/0x4fb > [ 2.891329] secondary_startup_64_no_verify+0xb0/0xbb >=20 > Since, the hypervisor already provides the VP assist page for root > partition, we need to memremaps the memory from hypervisor for root s/memremaps/memremap/ > kernel to use. The mapping is done in hv_cpu_init during bringup and > is unmaped in hv_cpu_die during teardown. >=20 > Signed-off-by: Praveen Kumar > --- > arch/x86/hyperv/hv_init.c | 53 ++++++++++++++++++++++++++------------- > 1 file changed, 36 insertions(+), 17 deletions(-) >=20 > changelog: > v1: initial patch > v2: commit message changes, removal of HV_MSR_APIC_ACCESS_AVAILABLE > check and addition of null check before reading the VP assist MSR > for root partition >=20 > --- > diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c > index 6f247e7e07eb..ffd3d3b37235 100644 > --- a/arch/x86/hyperv/hv_init.c > +++ b/arch/x86/hyperv/hv_init.c > @@ -55,26 +55,41 @@ static int hv_cpu_init(unsigned int cpu) > return 0; >=20 > /* > - * The VP ASSIST PAGE is an "overlay" page (see Hyper-V TLFS's Section > - * 5.2.1 "GPA Overlay Pages"). Here it must be zeroed out to make sure > - * we always write the EOI MSR in hv_apic_eoi_write() *after* the > - * EOI optimization is disabled in hv_cpu_die(), otherwise a CPU may > - * not be stopped in the case of CPU offlining and the VM will hang. > + * For Root partition we need to map the hypervisor VP ASSIST PAGE > + * instead of allocating a new page. > */ > - if (!*hvp) { > - *hvp =3D __vmalloc(PAGE_SIZE, GFP_KERNEL | __GFP_ZERO); > - } > + if (hv_root_partition) { > + union hv_x64_msr_hypercall_contents hypercall_msr; This isn't the correct variable type to be using here. Union hv_x64_msr_hypercall_contents is specifically for HV_X64_MSR_HYPERCALL. It also happens to be correct for HV_X64_MSR_VP_ASSIST_PAGE, but the layout of the two MSRs could diverge in the future. Instead of using this = union, I would suggest just reading into a u64, and then mask as needed. The code= in the non-root-partition branch of the 'if' statement is similarly open codin= g the needed shifting/masking to construct the value to write. Or you could define another union specifically for the VP Assist page MSR. I'm OK with either approach. Michael > + > + rdmsrl(HV_X64_MSR_VP_ASSIST_PAGE, hypercall_msr.as_uint64); > + /* remapping to root partition address space */ > + if (!*hvp) > + *hvp =3D memremap(hypercall_msr.guest_physical_address << > + HV_X64_MSR_VP_ASSIST_PAGE_ADDRESS_SHIFT, > + PAGE_SIZE, MEMREMAP_WB); > + WARN_ON(!(*hvp)); > + } else { > + /* > + * The VP ASSIST PAGE is an "overlay" page (see Hyper-V TLFS's > + * Section 5.2.1 "GPA Overlay Pages"). Here it must be zeroed > + * out to make sure we always write the EOI MSR in > + * hv_apic_eoi_write() *after* theEOI optimization is disabled > + * in hv_cpu_die(), otherwise a CPU may not be stopped in the > + * case of CPU offlining and the VM will hang. > + */ > + if (!*hvp) > + *hvp =3D __vmalloc(PAGE_SIZE, GFP_KERNEL | __GFP_ZERO); >=20 > - if (*hvp) { > - u64 val; > + if (*hvp) { > + u64 val; >=20 > - val =3D vmalloc_to_pfn(*hvp); > - val =3D (val << HV_X64_MSR_VP_ASSIST_PAGE_ADDRESS_SHIFT) | > - HV_X64_MSR_VP_ASSIST_PAGE_ENABLE; > + val =3D vmalloc_to_pfn(*hvp); > + val =3D (val << HV_X64_MSR_VP_ASSIST_PAGE_ADDRESS_SHIFT) | > + HV_X64_MSR_VP_ASSIST_PAGE_ENABLE; >=20 > - wrmsrl(HV_X64_MSR_VP_ASSIST_PAGE, val); > + wrmsrl(HV_X64_MSR_VP_ASSIST_PAGE, val); > + } > } > - > return 0; > } >=20 > @@ -170,8 +185,12 @@ static int hv_cpu_die(unsigned int cpu) >=20 > hv_common_cpu_die(cpu); >=20 > - if (hv_vp_assist_page && hv_vp_assist_page[cpu]) > - wrmsrl(HV_X64_MSR_VP_ASSIST_PAGE, 0); > + if (hv_vp_assist_page && hv_vp_assist_page[cpu]) { > + if (hv_root_partition) > + memunmap(hv_vp_assist_page[cpu]); > + else > + wrmsrl(HV_X64_MSR_VP_ASSIST_PAGE, 0); > + } >=20 > if (hv_reenlightenment_cb =3D=3D NULL) > return 0; > -- > 2.25.1