From: Roman Kisel <[email protected]> Sent: Friday, October 3, 2025
3:27 PM
>
> hv_set_non_nested_msr() has special handling for SINT MSRs
> when a paravisor is present. In addition to updating the MSR on the
> host, the mirror MSR in the paravisor is updated, including with the
> proxy bit. But with Confidential VMBus, the proxy bit must not be
> used, so add a special case to skip it.
>
> Signed-off-by: Roman Kisel <[email protected]>
> Reviewed-by: Alok Tiwari <[email protected]>
> Reviewed-by: Tianyu Lan <[email protected]>
> ---
> arch/x86/kernel/cpu/mshyperv.c | 29 +++++++++++++++++++++++++----
> drivers/hv/hv_common.c | 5 +++++
> include/asm-generic/mshyperv.h | 1 +
> 3 files changed, 31 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index af5a3bbbca9f..b410b930938a 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -28,6 +28,7 @@
> #include <asm/apic.h>
> #include <asm/timer.h>
> #include <asm/reboot.h>
> +#include <asm/msr.h>
> #include <asm/nmi.h>
> #include <clocksource/hyperv_timer.h>
> #include <asm/msr.h>
> @@ -38,6 +39,12 @@
> bool hv_nested;
> struct ms_hyperv_info ms_hyperv;
>
> +/*
> + * When running with the paravisor, controls proxying the synthetic
> interrupts
> + * from the host
> + */
> +static bool hv_para_sint_proxy;
This needs to move down a few lines and be under the #if
IS_ENABLED(CONFIG_HYPERV)
in order to eliminate the "unused variable" warning reported by the kernel test
robot.
> +
> /* Used in modules via hv_do_hypercall(): see
> arch/x86/include/asm/mshyperv.h */
> bool hyperv_paravisor_present __ro_after_init;
> EXPORT_SYMBOL_GPL(hyperv_paravisor_present);
> @@ -79,17 +86,31 @@ EXPORT_SYMBOL_GPL(hv_get_non_nested_msr);
> void hv_set_non_nested_msr(unsigned int reg, u64 value)
> {
> if (hv_is_synic_msr(reg) && ms_hyperv.paravisor_present) {
> + /* The hypervisor will get the intercept. */
> hv_ivm_msr_write(reg, value);
>
> - /* Write proxy bit via wrmsl instruction */
> - if (hv_is_sint_msr(reg))
> - wrmsrq(reg, value | 1 << 20);
> + /* Using wrmsrq so the following goes to the paravisor. */
> + if (hv_is_sint_msr(reg)) {
> + union hv_synic_sint sint = { .as_uint64 = value };
> +
> + sint.proxy = hv_para_sint_proxy;
> + native_wrmsrq(reg, sint.as_uint64);
> + }
> } else {
> - wrmsrq(reg, value);
> + native_wrmsrq(reg, value);
> }
> }
> EXPORT_SYMBOL_GPL(hv_set_non_nested_msr);
>
> +/*
> + * Enable or disable proxying synthetic interrupts
> + * to the paravisor.
> + */
> +void hv_para_set_sint_proxy(bool enable)
> +{
> + hv_para_sint_proxy = enable;
> +}
> +
> /*
> * Get the SynIC register value from the paravisor.
> */
> diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
> index 8756ca834546..1a5c7a358971 100644
> --- a/drivers/hv/hv_common.c
> +++ b/drivers/hv/hv_common.c
> @@ -716,6 +716,11 @@ u64 __weak hv_tdx_hypercall(u64 control, u64 param1, u64
> param2)
> }
> EXPORT_SYMBOL_GPL(hv_tdx_hypercall);
>
> +void __weak hv_para_set_sint_proxy(bool enable)
> +{
> +}
> +EXPORT_SYMBOL_GPL(hv_para_set_sint_proxy);
> +
> u64 __weak hv_para_get_synic_register(unsigned int reg)
> {
> return ~0ULL;
> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
> index c010059f1518..3955ba6d60b8 100644
> --- a/include/asm-generic/mshyperv.h
> +++ b/include/asm-generic/mshyperv.h
> @@ -298,6 +298,7 @@ bool hv_is_isolation_supported(void);
> bool hv_isolation_type_snp(void);
> u64 hv_ghcb_hypercall(u64 control, void *input, void *output, u32
> input_size);
> u64 hv_tdx_hypercall(u64 control, u64 param1, u64 param2);
> +void hv_para_set_sint_proxy(bool enable);
> u64 hv_para_get_synic_register(unsigned int reg);
> void hv_para_set_synic_register(unsigned int reg, u64 val);
> void hyperv_cleanup(void);
> --
> 2.43.0
>
