RE: [PATCH v3 12/13] x86/hyperv/vtl: Mark the wakeup mailbox page as private

Michael Kelley
2025-05-20T01:34:01Z

From: Ricardo Neri <ricardo.neri-calderon@linux.intel.com> Sent: Saturday, May 3, 2025 12:15 PM
>
> From: Yunhong Jiang <yunhong.jiang@linux.intel.com>
>
> The current code maps MMIO devices as shared (decrypted) by default in a
> confidential computing VM.
>
> In a TDX environment, secondary CPUs are booted using the Multiprocessor
> Wakeup Structure defined in the ACPI specification. The virtual firmware
> and the operating system function in the guest context, without
> intervention from the VMM. Map the physical memory of the mailbox as
> private. Use the is_private_mmio() callback.
>
> Signed-off-by: Yunhong Jiang <yunhong.jiang@linux.intel.com>
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
> ---
> Changes since v2:
> - Use the new helper function get_mp_wakeup_mailbox_paddr().
> - Edited the commit message for clarity.
>
> Changes since v1:
> - Added the helper function within_page() to improve readability
> - Override the is_private_mmio() callback when detecting a TDX
> environment. The address of the mailbox is checked in
> hv_is_private_mmio_tdx().
> ---
> arch/x86/hyperv/hv_vtl.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/arch/x86/hyperv/hv_vtl.c b/arch/x86/hyperv/hv_vtl.c
> index 8b497c8292d3..cd48bedd21f0 100644
> --- a/arch/x86/hyperv/hv_vtl.c
> +++ b/arch/x86/hyperv/hv_vtl.c
> @@ -54,6 +54,18 @@ static void __noreturn hv_vtl_restart(char __maybe_unused *cmd)
> hv_vtl_emergency_restart();
> }
>
> +static inline bool within_page(u64 addr, u64 start)
> +{
> + return addr >= start && addr < (start + PAGE_SIZE);
> +}
> +
> +static bool hv_vtl_is_private_mmio_tdx(u64 addr)
> +{
> + u64 mb_addr = get_mp_wakeup_mailbox_paddr();
> +
> + return mb_addr && within_page(addr, mb_addr);
> +}
> +
> void __init hv_vtl_init_platform(void)
> {
> pr_info("Linux runs in Hyper-V Virtual Trust Level\n");
> @@ -61,6 +73,8 @@ void __init hv_vtl_init_platform(void)
> /* There is no paravisor present if we are here. */
> if (hv_isolation_type_tdx()) {
> x86_init.resources.realmode_limit = SZ_4G;
> + x86_platform.hyper.is_private_mmio = hv_vtl_is_private_mmio_tdx;
> +
> } else {
> x86_platform.realmode_reserve = x86_init_noop;
> x86_platform.realmode_init = x86_init_noop;
> --
> 2.43.0

Reviewed-by: Michael Kelley <mhklinux@outlook.com>