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Date: Tue, 15 Nov 2022 10:57:10 +0530
From: Jinank Jain <jinankjain@...ux.microsoft.com>
To: Anirudh Rayabharam <anrayabh@...ux.microsoft.com>
Cc: jinankjain@...rosoft.com, kys@...rosoft.com,
haiyangz@...rosoft.com, wei.liu@...nel.org, decui@...rosoft.com,
tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
arnd@...db.de, peterz@...radead.org, jpoimboe@...nel.org,
seanjc@...gle.com, kirill.shutemov@...ux.intel.com,
ak@...ux.intel.com, sathyanarayanan.kuppuswamy@...ux.intel.com,
linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-arch@...r.kernel.org, mikelley@...rosoft.com
Subject: Re: [PATCH v3 2/5] Drivers: hv: Setup synic registers in case of
nested root partition
On 11/4/2022 4:11 PM, Anirudh Rayabharam wrote:
> On Thu, Nov 03, 2022 at 01:04:04PM +0000, Jinank Jain wrote:
>> Child partitions are free to allocate SynIC message and event page but in
>> case of root partition it must use the pages allocated by Microsoft
>> Hypervisor (MSHV). Base address for these pages can be found using
>> synthetic MSRs exposed by MSHV. There is a slight difference in those MSRs
>> for nested vs non-nested root partition.
>>
>> Signed-off-by: Jinank Jain <jinankjain@...ux.microsoft.com>
>> ---
>> arch/x86/include/asm/hyperv-tlfs.h | 11 +++++++++++
>> arch/x86/include/asm/mshyperv.h | 24 ++++++++++++++++++++++++
>> drivers/hv/hv.c | 18 +++++++++++++-----
>> 3 files changed, 48 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h
>> index d9a611565859..0319091e2019 100644
>> --- a/arch/x86/include/asm/hyperv-tlfs.h
>> +++ b/arch/x86/include/asm/hyperv-tlfs.h
>> @@ -225,6 +225,17 @@ enum hv_isolation_type {
>> #define HV_REGISTER_SINT14 0x4000009E
>> #define HV_REGISTER_SINT15 0x4000009F
>>
>> +/*
>> + * Define synthetic interrupt controller model specific registers for
>> + * nested hypervisor.
>> + */
>> +#define HV_REGISTER_NESTED_SCONTROL 0x40001080
>> +#define HV_REGISTER_NESTED_SVERSION 0x40001081
>> +#define HV_REGISTER_NESTED_SIEFP 0x40001082
>> +#define HV_REGISTER_NESTED_SIMP 0x40001083
>> +#define HV_REGISTER_NESTED_EOM 0x40001084
>> +#define HV_REGISTER_NESTED_SINT0 0x40001090
>> +
>> /*
>> * Synthetic Timer MSRs. Four timers per vcpu.
>> */
>> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
>> index 3c39923e5969..b0f16d06a0c5 100644
>> --- a/arch/x86/include/asm/mshyperv.h
>> +++ b/arch/x86/include/asm/mshyperv.h
>> @@ -200,10 +200,31 @@ static inline bool hv_is_synic_reg(unsigned int reg)
>> return false;
>> }
>>
>> +static inline unsigned int hv_get_nested_reg(unsigned int reg)
>> +{
>> + switch (reg) {
>> + case HV_REGISTER_SIMP:
>> + return HV_REGISTER_NESTED_SIMP;
>> + case HV_REGISTER_NESTED_SIEFP:
>> + return HV_REGISTER_SIEFP;
>> + case HV_REGISTER_SCONTROL:
>> + return HV_REGISTER_NESTED_SCONTROL;
>> + case HV_REGISTER_SINT0:
>> + return HV_REGISTER_NESTED_SINT0;
>> + case HV_REGISTER_EOM:
>> + return HV_REGISTER_NESTED_EOM;
>> + default:
>> + return reg;
>> + }
>> +}
>> +
>> static inline u64 hv_get_register(unsigned int reg)
>> {
>> u64 value;
>>
>> + if (hv_nested)
>> + reg = hv_get_nested_reg(reg);
> With this change the nested root cannot read it's own SynIC MSRs using
> this method. It will always read the SynIC MSRs corresponding to the
> nesting hypervisor. Similar is the case with hv_set_register.
>
> Will there never be a need for nested root to read/write it's own SynIC
> MSRs? For e.g. to set up inter partition communication at the L2 level.
>
> Anirudh.
As far as the current use case goes I doubt there would be a use case
like that. In future if such a scneario arises, I think we can add an
additional parameter to hv_(get|set)_register, called nested and
depending on the value of that parameter we can return the value of
nested or non-nested registers. This would be very similar to the design
I posted in revision 1 of this patch series.
Jinank.
>
>> +
>> if (hv_is_synic_reg(reg) && hv_isolation_type_snp())
>> hv_ghcb_msr_read(reg, &value);
>> else
>> @@ -213,6 +234,9 @@ static inline u64 hv_get_register(unsigned int reg)
>>
>> static inline void hv_set_register(unsigned int reg, u64 value)
>> {
>> + if (hv_nested)
>> + reg = hv_get_nested_reg(reg);
>> +
>> if (hv_is_synic_reg(reg) && hv_isolation_type_snp()) {
>> hv_ghcb_msr_write(reg, value);
>>
>> diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
>> index 4d6480d57546..9e1eb50cc76f 100644
>> --- a/drivers/hv/hv.c
>> +++ b/drivers/hv/hv.c
>> @@ -147,7 +147,7 @@ int hv_synic_alloc(void)
>> * Synic message and event pages are allocated by paravisor.
>> * Skip these pages allocation here.
>> */
>> - if (!hv_isolation_type_snp()) {
>> + if (!hv_isolation_type_snp() && !hv_root_partition) {
>> hv_cpu->synic_message_page =
>> (void *)get_zeroed_page(GFP_ATOMIC);
>> if (hv_cpu->synic_message_page == NULL) {
>> @@ -188,8 +188,16 @@ void hv_synic_free(void)
>> struct hv_per_cpu_context *hv_cpu
>> = per_cpu_ptr(hv_context.cpu_context, cpu);
>>
>> - free_page((unsigned long)hv_cpu->synic_event_page);
>> - free_page((unsigned long)hv_cpu->synic_message_page);
>> + if (hv_root_partition) {
>> + if (hv_cpu->synic_event_page != NULL)
>> + memunmap(hv_cpu->synic_event_page);
>> +
>> + if (hv_cpu->synic_message_page != NULL)
>> + memunmap(hv_cpu->synic_message_page);
>> + } else {
>> + free_page((unsigned long)hv_cpu->synic_event_page);
>> + free_page((unsigned long)hv_cpu->synic_message_page);
>> + }
>> free_page((unsigned long)hv_cpu->post_msg_page);
>> }
>>
>> @@ -216,7 +224,7 @@ void hv_synic_enable_regs(unsigned int cpu)
>> simp.as_uint64 = hv_get_register(HV_REGISTER_SIMP);
>> simp.simp_enabled = 1;
>>
>> - if (hv_isolation_type_snp()) {
>> + if (hv_isolation_type_snp() || hv_root_partition) {
>> hv_cpu->synic_message_page
>> = memremap(simp.base_simp_gpa << HV_HYP_PAGE_SHIFT,
>> HV_HYP_PAGE_SIZE, MEMREMAP_WB);
>> @@ -233,7 +241,7 @@ void hv_synic_enable_regs(unsigned int cpu)
>> siefp.as_uint64 = hv_get_register(HV_REGISTER_SIEFP);
>> siefp.siefp_enabled = 1;
>>
>> - if (hv_isolation_type_snp()) {
>> + if (hv_isolation_type_snp() || hv_root_partition) {
>> hv_cpu->synic_event_page =
>> memremap(siefp.base_siefp_gpa << HV_HYP_PAGE_SHIFT,
>> HV_HYP_PAGE_SIZE, MEMREMAP_WB);
>> --
>> 2.25.1
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