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Date:   Mon, 2 Aug 2021 12:51:33 +0000
From:   Wei Liu <wei.liu@kernel.org>
To:     Praveen Kumar <kumarpraveen@linux.microsoft.com>
Cc:     linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org,
        kys@microsoft.com, haiyangz@microsoft.com, sthemmin@microsoft.com,
        wei.liu@kernel.org, decui@microsoft.com, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com,
        viremana@linux.microsoft.com, sunilmut@microsoft.com,
        nunodasneves@linux.microsoft.com
Subject: Re: [PATCH v5] hyperv: root partition faults writing to VP ASSIST
 MSR PAGE
Message-ID: <20210802125133.ci2jlg32mdfd5xds@liuwe-devbox-debian-v2>
References: <20210731120519.17154-1-kumarpraveen@linux.microsoft.com>
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In-Reply-To: <20210731120519.17154-1-kumarpraveen@linux.microsoft.com>
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On Sat, Jul 31, 2021 at 05:35:19PM +0530, Praveen Kumar wrote:
> 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.
> 
> [ 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
> 
> Since, the hypervisor already provides the VP assist page for root
> partition, we need to memremap the memory from hypervisor for root
> kernel to use. The mapping is done in hv_cpu_init during bringup and
> is unmaped in hv_cpu_die during teardown.
> 
> Signed-off-by: Praveen Kumar <kumarpraveen@linux.microsoft.com>

Looks good. I can fix a few styling issues in code and comments when I
commit this patch.

Wei.