On 20-07-2021 16:50, Wei Liu wrote:
> The commit message needs a bit of work.
>
> On Tue, Jul 20, 2021 at 12:21:26AM +0530, Praveen Kumar wrote:
>> The root partition is not supposed to write to VP ASSIST PAGE as this MSR
>> is specific to Guest VP, and thus below stack is observed.
>>
>
> Yes, root kernel is supposed to write to this MSR, but that's not
> because this MSR is specific to children (guest) partitions. It is just
> that for root this is read-only.
>
> You should mention VP assist pages for root are pre-determined by the
> hypervisor. Root kernel is not allowed to change them to different
> locations.
>
>> [ 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
>>
>> Root partition actually shares the VP ASSIST page with hypervisor, and
>
> So do children partitions. This page is by design shared between
> hypervisor and any partitions that use it.
>
Sure, will send updated commit log with these information in V2
>> thus as a solution, this patch memremaps the memory from hypervisor
>> during hv_cpu_init and unmaps during hv_cpu_die calls.
>>
>> Further, this patch also resolve some error handling and checkpatch
>> errors
>>
>> Signed-off-by: Praveen Kumar <kumarpraveen@xxxxxxxxxxxxxxxxxxx>
>> ---
>> arch/x86/hyperv/hv_init.c | 57 +++++++++++++++++++++++++++------------
>> 1 file changed, 40 insertions(+), 17 deletions(-)
>>
>> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
>> index 6f247e7e07eb..292b17e0b173 100644
>> --- a/arch/x86/hyperv/hv_init.c
>> +++ b/arch/x86/hyperv/hv_init.c
>> @@ -44,7 +44,7 @@ EXPORT_SYMBOL_GPL(hv_vp_assist_page);
>>
>> static int hv_cpu_init(unsigned int cpu)
>> {
>> - struct hv_vp_assist_page **hvp = &hv_vp_assist_page[smp_processor_id()];
>> + struct hv_vp_assist_page **hvp = NULL;
>> int ret;
>>
>> ret = hv_common_cpu_init(cpu);
>> @@ -54,25 +54,43 @@ static int hv_cpu_init(unsigned int cpu)
>> if (!hv_vp_assist_page)
>> return 0;
>>
>> + hvp = &hv_vp_assist_page[smp_processor_id()];
>> +
>
> Why is this needed? Is it because of checkpatch?
I think this is not required.
>
>> /*
>> - * 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 = __vmalloc(PAGE_SIZE, GFP_KERNEL | __GFP_ZERO);
>> - }
>
> This path suggests that it is possible to enter this function with *hvp
> already set.
>
> The new path for root is missing this check.
Will add similar check for root partition as well. thanks.
>
>> + if (hv_root_partition &&
>> + ms_hyperv.features & HV_MSR_APIC_ACCESS_AVAILABLE) {
>
> Is HV_MSR_APIC_ACCESS_AVAILABLE a root only flag? Shouldn't non-root
> kernel check this too?
Yes, you are right. Will update this in v2. thanks.
>
> Wei.
>
Regards,
~Praveen.
