linux-kernel - RE: [PATCH v4 6/6] x86/hyperv: Fix serial console interrupts for TDX guests

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <BYAPR21MB1688798EA7DD5ED309BAE0F6D79A9@BYAPR21MB1688.namprd21.prod.outlook.com>
Date:   Tue, 11 Apr 2023 17:13:49 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Dexuan Cui <decui@...rosoft.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "arnd@...db.de" <arnd@...db.de>, "bp@...en8.de" <bp@...en8.de>,
        "brijesh.singh@....com" <brijesh.singh@....com>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "jane.chu@...cle.com" <jane.chu@...cle.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        KY Srinivasan <kys@...rosoft.com>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "luto@...nel.org" <luto@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "seanjc@...gle.com" <seanjc@...gle.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        "x86@...nel.org" <x86@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>
Subject: RE: [PATCH v4 6/6] x86/hyperv: Fix serial console interrupts for TDX
 guests

From: Dexuan Cui <decui@...rosoft.com> Sent: Saturday, April 8, 2023 1:48 PM
> 
> When a TDX guest runs on Hyper-V, the UEFI firmware sets the HW_REDUCED
> flag, and consequently ttyS0 interrupts can't work. Fix the issue by
> overriding x86_init.acpi.reduced_hw_early_init().
> 
> Signed-off-by: Dexuan Cui <decui@...rosoft.com>
> ---
> 
> Changes since v1:
>     None.
> 
>  arch/x86/kernel/cpu/mshyperv.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index e9106c9d92f81..deedced0f2bb0 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -318,6 +318,26 @@ static void __init hv_smp_prepare_cpus(unsigned int max_cpus)
>  }
>  #endif
> 
> +/*
> + * When a TDX guest runs on Hyper-V, the firmware sets the HW_REDUCED flag: see
> + * acpi_tb_create_local_fadt(). Consequently ttyS0 interrupts can't work because
> + * request_irq() -> ... -> irq_to_desc() returns NULL for ttyS0. This happens
> + * because mp_config_acpi_legacy_irqs() sees a nr_legacy_irqs() of 0, so it
> + * doesn't initialize the array 'mp_irqs[]', and later setup_IO_APIC_irqs() ->
> + * find_irq_entry() fails to find the legacy irqs from the array, and hence
> + * doesn't create the necessary irq description info.
> + *
> + * Copy arch/x86/kernel/acpi/boot.c: acpi_generic_reduced_hw_init() but doesn't
> + * change 'legacy_pic', so it keeps its default value 'default_legacy_pic' in
> + * mp_config_acpi_legacy_irqs(), which sees a non-zero nr_legacy_irqs(), and
> + * eventually serial console interrupts can work properly.

I had a little trouble parsing this comment.  Slightly better wording is:

    * Clone arch/x86/kernel/acpi/boot.c: acpi_generic_reduced_hw_init() here,
    * except don't change 'legacy_pic'.  It keeps its default value 'default_legacy_pic'.
    * mp_config_acpi_legacy_irqs() sees a non-zero nr_legacy_irqs(), and
    * eventually serial console interrupts can work properly.

Otherwise,

Reviewed-by: Michael Kelley <mikelley@...rosoft.com>

> + */
> +static void __init reduced_hw_init(void)
> +{
> +	x86_init.timers.timer_init	= x86_init_noop;
> +	x86_init.irqs.pre_vector_init	= x86_init_noop;
> +}
> +
>  static void __init ms_hyperv_init_platform(void)
>  {
>  	int hv_max_functions_eax;
> @@ -425,6 +445,8 @@ static void __init ms_hyperv_init_platform(void)
> 
>  			/* A TDX VM must use x2APIC and doesn't use lazy EOI */
>  			ms_hyperv.hints &= ~HV_X64_APIC_ACCESS_RECOMMENDED;
> +
> +			x86_init.acpi.reduced_hw_early_init = reduced_hw_init;
>  		}
>  	}
> 
> --
> 2.25.1