From: Roman Kisel <romank@xxxxxxxxxxxxxxxxxxx> Sent: Wednesday, August 27, 2025 6:06 PM
>
> The confidential VMBus runs with the paravisor SynIC and requires
> configuring it with the paravisor.
>
> Add the functions for configuring the paravisor SynIC. Update
> overall SynIC initialization logic to initialize the SynIC if it
> is present. Finally, break out SynIC interrupt enable/disable
> code into separate functions so that SynIC interrupts can be
> enabled or disabled via the paravisor instead of the hypervisor
> if the paravisor SynIC is present.
>
> Signed-off-by: Roman Kisel <romank@xxxxxxxxxxxxxxxxxxx>
> Reviewed-by: Michael Kelley <mhklinux@xxxxxxxxxxx>
> ---
> drivers/hv/hv.c | 192 +++++++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 180 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
> index efe161d95b25..78ae3e1381dc 100644
> --- a/drivers/hv/hv.c
> +++ b/drivers/hv/hv.c
> @@ -281,9 +281,8 @@ void hv_hyp_synic_enable_regs(unsigned int cpu)
> union hv_synic_simp simp;
> union hv_synic_siefp siefp;
> union hv_synic_sint shared_sint;
> - union hv_synic_scontrol sctrl;
>
> - /* Setup the Synic's message page */
> + /* Setup the Synic's message page with the hypervisor. */
> simp.as_uint64 = hv_get_msr(HV_MSR_SIMP);
> simp.simp_enabled = 1;
>
> @@ -302,7 +301,7 @@ void hv_hyp_synic_enable_regs(unsigned int cpu)
>
> hv_set_msr(HV_MSR_SIMP, simp.as_uint64);
>
> - /* Setup the Synic's event page */
> + /* Setup the Synic's event page with the hypervisor. */
> siefp.as_uint64 = hv_get_msr(HV_MSR_SIEFP);
> siefp.siefp_enabled = 1;
>
> @@ -330,6 +329,11 @@ void hv_hyp_synic_enable_regs(unsigned int cpu)
> shared_sint.masked = false;
> shared_sint.auto_eoi = hv_recommend_using_aeoi();
> hv_set_msr(HV_MSR_SINT0 + VMBUS_MESSAGE_SINT, shared_sint.as_uint64);
> +}
> +
> +static void hv_hyp_synic_enable_interrupts(void)
> +{
> + union hv_synic_scontrol sctrl;
>
> /* Enable the global synic bit */
> sctrl.as_uint64 = hv_get_msr(HV_MSR_SCONTROL);
> @@ -338,13 +342,101 @@ void hv_hyp_synic_enable_regs(unsigned int cpu)
> hv_set_msr(HV_MSR_SCONTROL, sctrl.as_uint64);
> }
>
> +/*
> + * The paravisor might not support proxying SynIC, and this
> + * function may fail.
> + */
> +static int hv_para_synic_enable_regs(unsigned int cpu)
> +{
> + int err;
> + union hv_synic_simp simp;
> + union hv_synic_siefp siefp;
> + struct hv_per_cpu_context *hv_cpu
> + = per_cpu_ptr(hv_context.cpu_context, cpu);
> +
> + /* Setup the Synic's message page with the paravisor. */
> + err = hv_para_get_synic_register(HV_MSR_SIMP, &simp.as_uint64);
> + if (err)
> + return err;
> + simp.simp_enabled = 1;
> + simp.base_simp_gpa = virt_to_phys(hv_cpu->para_synic_message_page)
> + >> HV_HYP_PAGE_SHIFT;
> + err = hv_para_set_synic_register(HV_MSR_SIMP, simp.as_uint64);
> + if (err)
> + return err;
> +
> + /* Setup the Synic's event page with the paravisor. */
> + err = hv_para_get_synic_register(HV_MSR_SIEFP, &siefp.as_uint64);
> + if (err)
> + return err;
> + siefp.siefp_enabled = 1;
> + siefp.base_siefp_gpa = virt_to_phys(hv_cpu->para_synic_event_page)
> + >> HV_HYP_PAGE_SHIFT;
> + return hv_para_set_synic_register(HV_MSR_SIEFP, siefp.as_uint64);
> +}
> +
> +static int hv_para_synic_enable_interrupts(void)
> +{
> + union hv_synic_scontrol sctrl;
> + int err;
> +
> + /* Enable the global synic bit */
> + err = hv_para_get_synic_register(HV_MSR_SCONTROL, &sctrl.as_uint64);
> + if (err)
> + return err;
> + sctrl.enable = 1;
> +
> + return hv_para_set_synic_register(HV_MSR_SCONTROL, sctrl.as_uint64);
> +}
> +
> int hv_synic_init(unsigned int cpu)
> {
> + int err;
> +
> + /*
> + * The paravisor may not support the confidential VMBus,
> + * check on that first.
> + */
> + if (vmbus_is_confidential()) {
> + err = hv_para_synic_enable_regs(cpu);
> + if (err)
> + goto fail;
> + }
> +
> + /*
> + * The SINT is set in hv_hyp_synic_enable_regs() by calling
> + * hv_set_msr(). hv_set_msr() in turn has special case code for the
> + * SINT MSRs that write to the hypervisor version of the MSR *and*
> + * the paravisor version of the MSR (but *without* the proxy bit when
> + * VMBus is confidential).
> + *
> + * Then enable interrupts via the paravisor if VMBus is confidential,
> + * and otherwise via the hypervisor.
> + */
> +
> hv_hyp_synic_enable_regs(cpu);
> + if (vmbus_is_confidential()) {
> + err = hv_para_synic_enable_interrupts();
> + if (err)
> + goto fail;
> + } else
> + hv_hyp_synic_enable_interrupts();
>
> hv_stimer_legacy_init(cpu, VMBUS_MESSAGE_SINT);
>
> return 0;
> +
> +fail:
> + /*
> + * The failure may only come from enabling the paravisor SynIC.
> + * That in turn means that the confidential VMBus cannot be used
> + * which is not an error: the setup will be re-tried with the
> + * non-confidential VMBus.
Isn't this code comment now out-of-date? Retrying is no longer
implemented since the CPUID bit explicitly indicates if Confidential
VMBus is present.
This failure is fatal now, correct?
> + *
> + * We also don't bother attempting to reset the paravisor registers
> + * as something isn't working there anyway.
> + */
> + return err;
> }
>
> void hv_hyp_synic_disable_regs(unsigned int cpu)
> @@ -354,7 +446,6 @@ void hv_hyp_synic_disable_regs(unsigned int cpu)
> union hv_synic_sint shared_sint;
> union hv_synic_simp simp;
> union hv_synic_siefp siefp;
> - union hv_synic_scontrol sctrl;
>
> shared_sint.as_uint64 = hv_get_msr(HV_MSR_SINT0 +
> VMBUS_MESSAGE_SINT);
>
> @@ -366,7 +457,7 @@ void hv_hyp_synic_disable_regs(unsigned int cpu)
>
> simp.as_uint64 = hv_get_msr(HV_MSR_SIMP);
> /*
> - * In Isolation VM, sim and sief pages are allocated by
> + * In Isolation VM, simp and sief pages are allocated by
> * paravisor. These pages also will be used by kdump
> * kernel. So just reset enable bit here and keep page
> * addresses.
> @@ -396,14 +487,58 @@ void hv_hyp_synic_disable_regs(unsigned int cpu)
> }
>
> hv_set_msr(HV_MSR_SIEFP, siefp.as_uint64);
> +}
> +
> +static void hv_hyp_synic_disable_interrupts(void)
> +{
> + union hv_synic_scontrol sctrl;
>
> /* Disable the global synic bit */
> sctrl.as_uint64 = hv_get_msr(HV_MSR_SCONTROL);
> sctrl.enable = 0;
> hv_set_msr(HV_MSR_SCONTROL, sctrl.as_uint64);
> +}
>
> - if (vmbus_irq != -1)
> - disable_percpu_irq(vmbus_irq);
> +static void hv_para_synic_disable_regs(unsigned int cpu)
> +{
> + /*
> + * When a get/set register error is encountered, the function
> + * returns as the paravisor may not support these registers.
> + */
> + int err;
> + union hv_synic_simp simp;
> + union hv_synic_siefp siefp;
> +
> + /* Disable SynIC's message page in the paravisor. */
> + err = hv_para_get_synic_register(HV_MSR_SIMP, &simp.as_uint64);
> + if (err)
> + return;
> + simp.simp_enabled = 0;
> +
> + err = hv_para_set_synic_register(HV_MSR_SIMP, simp.as_uint64);
> + if (err)
> + return;
> +
> + /* Disable SynIC's event page in the paravisor. */
> + err = hv_para_get_synic_register(HV_MSR_SIEFP, &siefp.as_uint64);
> + if (err)
> + return;
> + siefp.siefp_enabled = 0;
> +
> + hv_para_set_synic_register(HV_MSR_SIEFP, siefp.as_uint64);
> +}
> +
> +static void hv_para_synic_disable_interrupts(void)
> +{
> + union hv_synic_scontrol sctrl;
> + int err;
> +
> + /* Disable the global synic bit */
> + err = hv_para_get_synic_register(HV_MSR_SCONTROL, &sctrl.as_uint64);
> + if (err)
> + return;
> + sctrl.enable = 0;
> + hv_para_set_synic_register(HV_MSR_SCONTROL, sctrl.as_uint64);
> }
>
> #define HV_MAX_TRIES 3
> @@ -416,16 +551,18 @@ void hv_hyp_synic_disable_regs(unsigned int cpu)
> * that the normal interrupt handling mechanism will find and process the channel
> interrupt
> * "very soon", and in the process clear the bit.
> */
> -static bool hv_synic_event_pending(void)
> +static bool __hv_synic_event_pending(union hv_synic_event_flags *event, int sint)
> {
> - struct hv_per_cpu_context *hv_cpu = this_cpu_ptr(hv_context.cpu_context);
> - union hv_synic_event_flags *event =
> - (union hv_synic_event_flags *)hv_cpu->hyp_synic_event_page +
> VMBUS_MESSAGE_SINT;
> - unsigned long *recv_int_page = event->flags; /* assumes VMBus version >=
> VERSION_WIN8 */
> + unsigned long *recv_int_page;
> bool pending;
> u32 relid;
> int tries = 0;
>
> + if (!event)
> + return false;
> +
> + event += sint;
> + recv_int_page = event->flags; /* assumes VMBus version >= VERSION_WIN8 */
> retry:
> pending = false;
> for_each_set_bit(relid, recv_int_page, HV_EVENT_FLAGS_COUNT) {
> @@ -442,6 +579,17 @@ static bool hv_synic_event_pending(void)
> return pending;
> }
>
> +static bool hv_synic_event_pending(void)
> +{
> + struct hv_per_cpu_context *hv_cpu = this_cpu_ptr(hv_context.cpu_context);
> + union hv_synic_event_flags *hyp_synic_event_page = hv_cpu-
> >hyp_synic_event_page;
> + union hv_synic_event_flags *para_synic_event_page = hv_cpu-
> >para_synic_event_page;
> +
> + return
> + __hv_synic_event_pending(hyp_synic_event_page,
> VMBUS_MESSAGE_SINT) ||
> + __hv_synic_event_pending(para_synic_event_page,
> VMBUS_MESSAGE_SINT);
> +}
> +
> static int hv_pick_new_cpu(struct vmbus_channel *channel)
> {
> int ret = -EBUSY;
> @@ -534,7 +682,27 @@ int hv_synic_cleanup(unsigned int cpu)
> always_cleanup:
> hv_stimer_legacy_cleanup(cpu);
>
> + /*
> + * First, disable the event and message pages
> + * used for communicating with the host, and then
> + * disable the host interrupts if VMBus is not
> + * confidential.
> + */
> hv_hyp_synic_disable_regs(cpu);
> + if (!vmbus_is_confidential())
> + hv_hyp_synic_disable_interrupts();
> +
> + /*
> + * Perform the same steps for the Confidential VMBus.
> + * The sequencing provides the guarantee that no data
> + * may be posted for processing before disabling interrupts.
> + */
> + if (vmbus_is_confidential()) {
> + hv_para_synic_disable_regs(cpu);
> + hv_para_synic_disable_interrupts();
> + }
> + if (vmbus_irq != -1)
> + disable_percpu_irq(vmbus_irq);
>
> return ret;
> }
> --
> 2.43.0
>
