RE: [PATCH v7 2/5] Drivers: hv: Setup synic registers in case of nested root partition

From: Michael Kelley (LINUX)
Date: Thu Dec 01 2022 - 23:00:40 EST

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In reply to: Jinank Jain: "[PATCH v7 2/5] Drivers: hv: Setup synic registers in case of nested root partition"
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From: Jinank Jain <jinankjain@xxxxxxxxxxxxxxxxxxx> Sent: Thursday, December 1, 2022 3:04 AM
>
> 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@xxxxxxxxxxxxxxxxxxx>
> ---
> arch/x86/include/asm/hyperv-tlfs.h | 11 ++++
> arch/x86/include/asm/mshyperv.h | 30 ++-------
> arch/x86/kernel/cpu/mshyperv.c | 69 +++++++++++++++++++++
> drivers/hv/hv.c | 99 ++++++++++++++++++++++--------
> include/asm-generic/mshyperv.h | 5 +-
> 5 files changed, 165 insertions(+), 49 deletions(-)
>
> diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h
> index 58c03d18c235..b5019becb618 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 61f0c206bff0..3197d49c888c 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -198,30 +198,10 @@ static inline bool hv_is_synic_reg(unsigned int reg)
> return false;
> }
>
> -static inline u64 hv_get_register(unsigned int reg)
> -{
> - u64 value;
> -
> - if (hv_is_synic_reg(reg) && hv_isolation_type_snp())
> - hv_ghcb_msr_read(reg, &value);
> - else
> - rdmsrl(reg, value);
> - return value;
> -}
> -
> -static inline void hv_set_register(unsigned int reg, u64 value)
> -{
> - if (hv_is_synic_reg(reg) && hv_isolation_type_snp()) {
> - hv_ghcb_msr_write(reg, value);
> -
> - /* Write proxy bit via wrmsl instruction */
> - if (reg >= HV_REGISTER_SINT0 &&
> - reg <= HV_REGISTER_SINT15)
> - wrmsrl(reg, value | 1 << 20);
> - } else {
> - wrmsrl(reg, value);
> - }
> -}
> +u64 hv_get_register(unsigned int reg);
> +void hv_set_register(unsigned int reg, u64 value);
> +u64 hv_get_nested_register(unsigned int reg);
> +void hv_set_nested_register(unsigned int reg, u64 value);
>
> #else /* CONFIG_HYPERV */
> static inline void hyperv_init(void) {}
> @@ -241,6 +221,8 @@ static inline int hyperv_flush_guest_mapping_range(u64 as,
> }
> static inline void hv_set_register(unsigned int reg, u64 value) { }
> static inline u64 hv_get_register(unsigned int reg) { return 0; }
> +static inline void hv_set_nested_register(unsigned int reg, u64 value) { }
> +static inline u64 hv_get_nested_register(unsigned int reg) { return 0; }
> static inline int hv_set_mem_host_visibility(unsigned long addr, int numpages,
> bool visible)
> {
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index f9b78d4829e3..f2f6e10301a8 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -41,7 +41,76 @@ bool hv_root_partition;
> bool hv_nested;
> struct ms_hyperv_info ms_hyperv;
>
> +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;
> + }

Just a question: You added #defines for 6 nested registers. But
the switch statement above maps only 5 registers. Is it intentional
that there's not a mapping for HV_REGISTER_SVERSION?

> +}
> +
> #if IS_ENABLED(CONFIG_HYPERV)
> +static u64 _hv_get_register(unsigned int reg, bool nested)
> +{
> + u64 value;
> +
> + if (nested)
> + reg = hv_get_nested_reg(reg);
> +
> + if (hv_is_synic_reg(reg) && hv_isolation_type_snp())
> + hv_ghcb_msr_read(reg, &value);
> + else
> + rdmsrl(reg, value);
> + return value;
> +}
> +
> +static void _hv_set_register(unsigned int reg, u64 value, bool nested)
> +{
> + if (nested)
> + reg = hv_get_nested_reg(reg);
> +
> + if (hv_is_synic_reg(reg) && hv_isolation_type_snp()) {
> + hv_ghcb_msr_write(reg, value);
> +
> + /* Write proxy bit via wrmsl instruction */
> + if (reg >= HV_REGISTER_SINT0 &&
> + reg <= HV_REGISTER_SINT15)
> + wrmsrl(reg, value | 1 << 20);
> + } else {
> + wrmsrl(reg, value);
> + }
> +}
> +
> +u64 hv_get_register(unsigned int reg)
> +{
> + return _hv_get_register(reg, false);
> +}
> +
> +void hv_set_register(unsigned int reg, u64 value)
> +{
> + _hv_set_register(reg, value, false);
> +}
> +
> +u64 hv_get_nested_register(unsigned int reg)
> +{
> + return _hv_get_register(reg, true);
> +}
> +
> +void hv_set_nested_register(unsigned int reg, u64 value)
> +{
> + _hv_set_register(reg, value, true);
> +}
> +
> static void (*vmbus_handler)(void);
> static void (*hv_stimer0_handler)(void);
> static void (*hv_kexec_handler)(void);
> diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
> index 4d6480d57546..0ed052f2423e 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);
> }
>
> @@ -213,10 +221,12 @@ void hv_synic_enable_regs(unsigned int cpu)
> union hv_synic_scontrol sctrl;
>
> /* Setup the Synic's message page */
> - simp.as_uint64 = hv_get_register(HV_REGISTER_SIMP);
> + simp.as_uint64 = hv_nested ? hv_get_nested_register(HV_REGISTER_SIMP) :
> + hv_get_register(HV_REGISTER_SIMP);

Unfortunately, this code and the similar places below will run into
problems on ARM64. Drivers/hv/hv.c is common code on all architectures
so it needs to compile and run on ARM64 as well as x86/x64. But there's
no hv_get_nested_register() defined or implemented on the ARM64 side,
so the code will fail to compile.

I think there's a better way to do this. Based on Nuno's comments, it
seems like there are two hv_get_register() functions needed:

1) Get the value of the register or its nested cousin, based on the value
of hv_nested. That's what you are explicitly coding here.
2) Get the value of the register. Don't access the nested cousin, regardless
of the value of hv_nested.

Based on how you coded things earlier, I'm assuming #1 is what you want to
use in most cases, and specifically here in drivers/hv/hv.c. That's good,
because #1 can hide the testing of hv_nested in the x86-specific
implementation of hv_get_register(), while the ARM64 version of
hv_get_register() continues to do whatever it does now with no changes.

I'm also assuming that #2 may be used in particular cases in the code
that is specifically related to nesting. Give the #2 version a different
name --- maybe hv_get_nonnested_register(), or something like that --
and use it only in code under arch/x86 that is related to nesting. That
way, ARM64 won't be affected.

Of course, the same approach applies to hv_set_register().

hv_get_register() and hv_get_nonnested_register() will obviously
share some code. But rather than calling a common function starting
with underscore like you've done above, let me suggest that
hv_get_register() test hv_nested and potentially do the translation,
then call hv_get_nonnested_register(). That way you'll end up
with just two functions instead of three as above with
hv_get_register(), hv_get_nested_register(), and _hv_get_register().

I haven't coded up any of this, so take it as a suggestion. There
could be some problem with it that I haven't seen, or my assumptions
might be wrong. But give it a try and see if it works out. I'm hoping
it can all be handled on the x86 side without having to add complexity
on the ARM64 side.

Michael

> +
> 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);
> @@ -227,13 +237,18 @@ void hv_synic_enable_regs(unsigned int cpu)
> >> HV_HYP_PAGE_SHIFT;
> }
>
> - hv_set_register(HV_REGISTER_SIMP, simp.as_uint64);
> + if (hv_nested)
> + hv_set_nested_register(HV_REGISTER_SIMP, simp.as_uint64);
> + else
> + hv_set_register(HV_REGISTER_SIMP, simp.as_uint64);
>
> /* Setup the Synic's event page */
> - siefp.as_uint64 = hv_get_register(HV_REGISTER_SIEFP);
> + siefp.as_uint64 = hv_nested ?
> + hv_get_nested_register(HV_REGISTER_SIEFP) :
> + 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);
> @@ -245,13 +260,19 @@ void hv_synic_enable_regs(unsigned int cpu)
> >> HV_HYP_PAGE_SHIFT;
> }
>
> - hv_set_register(HV_REGISTER_SIEFP, siefp.as_uint64);
> + if (hv_nested)
> + hv_set_nested_register(HV_REGISTER_SIEFP, siefp.as_uint64);
> + else
> + hv_set_register(HV_REGISTER_SIEFP, siefp.as_uint64);
>
> /* Setup the shared SINT. */
> if (vmbus_irq != -1)
> enable_percpu_irq(vmbus_irq, 0);
> - shared_sint.as_uint64 = hv_get_register(HV_REGISTER_SINT0 +
> - VMBUS_MESSAGE_SINT);
> + shared_sint.as_uint64 =
> + hv_nested ?
> + hv_get_nested_register(HV_REGISTER_SINT0 +
> + VMBUS_MESSAGE_SINT) :
> + hv_get_register(HV_REGISTER_SINT0 +
> VMBUS_MESSAGE_SINT);
>
> shared_sint.vector = vmbus_interrupt;
> shared_sint.masked = false;
> @@ -266,14 +287,22 @@ void hv_synic_enable_regs(unsigned int cpu)
> #else
> shared_sint.auto_eoi = 0;
> #endif
> - hv_set_register(HV_REGISTER_SINT0 + VMBUS_MESSAGE_SINT,
> + if (hv_nested)
> + hv_set_nested_register(HV_REGISTER_SINT0 +
> VMBUS_MESSAGE_SINT,
> + shared_sint.as_uint64);
> + else
> + hv_set_register(HV_REGISTER_SINT0 + VMBUS_MESSAGE_SINT,
> shared_sint.as_uint64);
> -
> /* Enable the global synic bit */
> - sctrl.as_uint64 = hv_get_register(HV_REGISTER_SCONTROL);
> + sctrl.as_uint64 = hv_nested ?
> + hv_get_nested_register(HV_REGISTER_SCONTROL) :
> + hv_get_register(HV_REGISTER_SCONTROL);
> sctrl.enable = 1;
>
> - hv_set_register(HV_REGISTER_SCONTROL, sctrl.as_uint64);
> + if (hv_nested)
> + hv_set_nested_register(HV_REGISTER_SCONTROL, sctrl.as_uint64);
> + else
> + hv_set_register(HV_REGISTER_SCONTROL, sctrl.as_uint64);
> }
>
> int hv_synic_init(unsigned int cpu)
> @@ -297,17 +326,25 @@ void hv_synic_disable_regs(unsigned int cpu)
> union hv_synic_siefp siefp;
> union hv_synic_scontrol sctrl;
>
> - shared_sint.as_uint64 = hv_get_register(HV_REGISTER_SINT0 +
> - VMBUS_MESSAGE_SINT);
> + shared_sint.as_uint64 =
> + hv_nested ?
> + hv_get_nested_register(HV_REGISTER_SINT0 +
> + VMBUS_MESSAGE_SINT) :
> + hv_get_register(HV_REGISTER_SINT0 +
> VMBUS_MESSAGE_SINT);
>
> shared_sint.masked = 1;
>
> /* Need to correctly cleanup in the case of SMP!!! */
> /* Disable the interrupt */
> - hv_set_register(HV_REGISTER_SINT0 + VMBUS_MESSAGE_SINT,
> + if (hv_nested)
> + hv_set_nested_register(HV_REGISTER_SINT0 +
> VMBUS_MESSAGE_SINT,
> + shared_sint.as_uint64);
> + else
> + hv_set_register(HV_REGISTER_SINT0 + VMBUS_MESSAGE_SINT,
> shared_sint.as_uint64);
>
> - simp.as_uint64 = hv_get_register(HV_REGISTER_SIMP);
> + simp.as_uint64 = hv_nested ? hv_get_nested_register(HV_REGISTER_SIMP) :
> + hv_get_register(HV_REGISTER_SIMP);
> /*
> * In Isolation VM, sim and sief pages are allocated by
> * paravisor. These pages also will be used by kdump
> @@ -320,9 +357,14 @@ void hv_synic_disable_regs(unsigned int cpu)
> else
> simp.base_simp_gpa = 0;
>
> - hv_set_register(HV_REGISTER_SIMP, simp.as_uint64);
> + if (hv_nested)
> + hv_set_nested_register(HV_REGISTER_SIMP, simp.as_uint64);
> + else
> + hv_set_register(HV_REGISTER_SIMP, simp.as_uint64);
>
> - siefp.as_uint64 = hv_get_register(HV_REGISTER_SIEFP);
> + siefp.as_uint64 = hv_nested ?
> + hv_get_nested_register(HV_REGISTER_SIEFP) :
> + hv_get_register(HV_REGISTER_SIEFP);
> siefp.siefp_enabled = 0;
>
> if (hv_isolation_type_snp())
> @@ -330,12 +372,21 @@ void hv_synic_disable_regs(unsigned int cpu)
> else
> siefp.base_siefp_gpa = 0;
>
> - hv_set_register(HV_REGISTER_SIEFP, siefp.as_uint64);
> + if (hv_nested)
> + hv_set_nested_register(HV_REGISTER_SIEFP, siefp.as_uint64);
> + else
> + hv_set_register(HV_REGISTER_SIEFP, siefp.as_uint64);
>
> /* Disable the global synic bit */
> - sctrl.as_uint64 = hv_get_register(HV_REGISTER_SCONTROL);
> + sctrl.as_uint64 = hv_nested ?
> + hv_get_nested_register(HV_REGISTER_SCONTROL) :
> + hv_get_register(HV_REGISTER_SCONTROL);
> sctrl.enable = 0;
> - hv_set_register(HV_REGISTER_SCONTROL, sctrl.as_uint64);
> +
> + if (hv_nested)
> + hv_set_nested_register(HV_REGISTER_SCONTROL, sctrl.as_uint64);
> + else
> + hv_set_register(HV_REGISTER_SCONTROL, sctrl.as_uint64);
>
> if (vmbus_irq != -1)
> disable_percpu_irq(vmbus_irq);
> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
> index f131027830c3..db0b5be1e087 100644
> --- a/include/asm-generic/mshyperv.h
> +++ b/include/asm-generic/mshyperv.h
> @@ -147,7 +147,10 @@ static inline void vmbus_signal_eom(struct hv_message *msg,
> u32 old_msg_type)
> * possibly deliver another msg from the
> * hypervisor
> */
> - hv_set_register(HV_REGISTER_EOM, 0);
> + if (hv_nested)
> + hv_set_nested_register(HV_REGISTER_EOM, 0);
> + else
> + hv_set_register(HV_REGISTER_EOM, 0);
> }
> }
>
> --
> 2.25.1

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In reply to: Jinank Jain: "[PATCH v7 2/5] Drivers: hv: Setup synic registers in case of nested root partition"
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