[RFC] x86/virt/tdx: Disable KEXEC in the presence of TDX

  TDX doesn't currently support kexec so disable the latter when TDX
is detected at boot time. If kexec must absolutely be supported then
TDX can be disabled from the bios.

Making this decision at run time rather than as a compile time option
allows distribution kernels to have both enabled and delegate to the
user whether they want to use TDX/Kexec.

Signed-off-by: Nikolay Borisov <nik.borisov@suse.com>
---

Sending as RFC as I don't know the reason why initially it was decided to
enforce the incompaibility between kexec/tdx at build time rather than runtime.

 arch/x86/Kconfig            | 1 -
 arch/x86/virt/vmx/tdx/tdx.c | 6 ++++++
 include/linux/kexec.h       | 1 +
 kernel/kexec_core.c         | 5 +++++
 4 files changed, 12 insertions(+), 1 deletion(-)

--
2.34.1
  

On Thu, 2024-01-18 at 18:01 +0200, Nikolay Borisov wrote:
> TDX doesn't currently support kexec so disable the latter when TDX
> is detected at boot time. If kexec must absolutely be supported then
> TDX can be disabled from the bios.
> 
> Making this decision at run time rather than as a compile time option
> allows distribution kernels to have both enabled and delegate to the
> user whether they want to use TDX/Kexec.
> 
> Signed-off-by: Nikolay Borisov <nik.borisov@suse.com>

Hi Nikolay,

Thanks for the patch.

I am working in progress on patches to make kexec() work with TDX.  I plan to
send them out soon (e.g., next week), but I think perhaps your patch is
reasonable before that is merged.

Acked-by: Kai Huang <kai.huang@intel.com>

> ---
> 
> Sending as RFC as I don't know the reason why initially it was decided to
> enforce the incompaibility between kexec/tdx at build time rather than runtime.
> 
>  arch/x86/Kconfig            | 1 -
>  arch/x86/virt/vmx/tdx/tdx.c | 6 ++++++
>  include/linux/kexec.h       | 1 +
>  kernel/kexec_core.c         | 5 +++++
>  4 files changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 92c03cb99b3e..6c2b620b40d8 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1973,7 +1973,6 @@ config INTEL_TDX_HOST
>  	depends on X86_X2APIC
>  	select ARCH_KEEP_MEMBLOCK
>  	depends on CONTIG_ALLOC
> -	depends on !KEXEC_CORE
>  	depends on X86_MCE
>  	help
>  	  Intel Trust Domain Extensions (TDX) protects guest VMs from malicious
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index 4d6826a76f78..270090bd7b5e 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -20,6 +20,7 @@
>  #include <linux/memblock.h>
>  #include <linux/memory.h>
>  #include <linux/minmax.h>
> +#include <linux/kexec.h>
>  #include <linux/sizes.h>
>  #include <linux/pfn.h>
>  #include <linux/align.h>
> @@ -1473,6 +1474,11 @@ void __init tdx_init(void)
>  		return;
>  	}
> 
> +#ifdef CONFIG_KEXEC_CORE
> +	kexec_disable();
> +	pr_info("Disable Kexec. Turn off TDX in the BIOS to use KEXEC.\n");
> +#endif
> +
>  #if defined(CONFIG_ACPI) && defined(CONFIG_SUSPEND)
>  	pr_info("Disable ACPI S3. Turn off TDX in the BIOS to use ACPI S3.\n");
>  	acpi_suspend_lowlevel = NULL;
> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> index 8227455192b7..c434c8569242 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -500,6 +500,7 @@ static inline int crash_hotplug_memory_support(void) { return 0; }
>  static inline unsigned int crash_get_elfcorehdr_size(void) { return 0; }
>  #endif
> 
> +extern void kexec_disable(void);
>  #else /* !CONFIG_KEXEC_CORE */
>  struct pt_regs;
>  struct task_struct;
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index be5642a4ec49..8d3a2a04ff4d 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -927,6 +927,11 @@ struct kimage *kexec_image;
>  struct kimage *kexec_crash_image;
>  static int kexec_load_disabled;
> 
> +void kexec_disable(void)
> +{
> +	kexec_load_disabled = 1;
> +}
> +
>  #ifdef CONFIG_SYSCTL
>  static int kexec_limit_handler(struct ctl_table *table, int write,
>  			       void *buffer, size_t *lenp, loff_t *ppos)
> --
> 2.34.1
> 
>
  

[Adding Kirill as he has a series in flight about KEXEC]

On 18.01.24 г. 23:31 ч., Huang, Kai wrote:
> On Thu, 2024-01-18 at 18:01 +0200, Nikolay Borisov wrote:
>> TDX doesn't currently support kexec so disable the latter when TDX
>> is detected at boot time. If kexec must absolutely be supported then
>> TDX can be disabled from the bios.
>>
>> Making this decision at run time rather than as a compile time option
>> allows distribution kernels to have both enabled and delegate to the
>> user whether they want to use TDX/Kexec.
>>
>> Signed-off-by: Nikolay Borisov <nik.borisov@suse.com>
> 
> Hi Nikolay,
> 
> Thanks for the patch.
> 
> I am working in progress on patches to make kexec() work with TDX.  I plan to
> send them out soon (e.g., next week), but I think perhaps your patch is
> reasonable before that is merged.

I thought Kirill's series rectifies this ?


> 
> Acked-by: Kai Huang <kai.huang@intel.com>
> 
>> ---
>>
>> Sending as RFC as I don't know the reason why initially it was decided to
>> enforce the incompaibility between kexec/tdx at build time rather than runtime.
>>
>>   arch/x86/Kconfig            | 1 -
>>   arch/x86/virt/vmx/tdx/tdx.c | 6 ++++++
>>   include/linux/kexec.h       | 1 +
>>   kernel/kexec_core.c         | 5 +++++
>>   4 files changed, 12 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index 92c03cb99b3e..6c2b620b40d8 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -1973,7 +1973,6 @@ config INTEL_TDX_HOST
>>   	depends on X86_X2APIC
>>   	select ARCH_KEEP_MEMBLOCK
>>   	depends on CONTIG_ALLOC
>> -	depends on !KEXEC_CORE
>>   	depends on X86_MCE
>>   	help
>>   	  Intel Trust Domain Extensions (TDX) protects guest VMs from malicious
>> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
>> index 4d6826a76f78..270090bd7b5e 100644
>> --- a/arch/x86/virt/vmx/tdx/tdx.c
>> +++ b/arch/x86/virt/vmx/tdx/tdx.c
>> @@ -20,6 +20,7 @@
>>   #include <linux/memblock.h>
>>   #include <linux/memory.h>
>>   #include <linux/minmax.h>
>> +#include <linux/kexec.h>
>>   #include <linux/sizes.h>
>>   #include <linux/pfn.h>
>>   #include <linux/align.h>
>> @@ -1473,6 +1474,11 @@ void __init tdx_init(void)
>>   		return;
>>   	}
>>
>> +#ifdef CONFIG_KEXEC_CORE
>> +	kexec_disable();
>> +	pr_info("Disable Kexec. Turn off TDX in the BIOS to use KEXEC.\n");
>> +#endif
>> +
>>   #if defined(CONFIG_ACPI) && defined(CONFIG_SUSPEND)
>>   	pr_info("Disable ACPI S3. Turn off TDX in the BIOS to use ACPI S3.\n");
>>   	acpi_suspend_lowlevel = NULL;
>> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
>> index 8227455192b7..c434c8569242 100644
>> --- a/include/linux/kexec.h
>> +++ b/include/linux/kexec.h
>> @@ -500,6 +500,7 @@ static inline int crash_hotplug_memory_support(void) { return 0; }
>>   static inline unsigned int crash_get_elfcorehdr_size(void) { return 0; }
>>   #endif
>>
>> +extern void kexec_disable(void);
>>   #else /* !CONFIG_KEXEC_CORE */
>>   struct pt_regs;
>>   struct task_struct;
>> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
>> index be5642a4ec49..8d3a2a04ff4d 100644
>> --- a/kernel/kexec_core.c
>> +++ b/kernel/kexec_core.c
>> @@ -927,6 +927,11 @@ struct kimage *kexec_image;
>>   struct kimage *kexec_crash_image;
>>   static int kexec_load_disabled;
>>
>> +void kexec_disable(void)
>> +{
>> +	kexec_load_disabled = 1;
>> +}
>> +
>>   #ifdef CONFIG_SYSCTL
>>   static int kexec_limit_handler(struct ctl_table *table, int write,
>>   			       void *buffer, size_t *lenp, loff_t *ppos)
>> --
>> 2.34.1
>>
>>
>
  

On Fri, 2024-01-19 at 02:49 +0200, Nikolay Borisov wrote:
> [Adding Kirill as he has a series in flight about KEXEC]
> 
> On 18.01.24 г. 23:31 ч., Huang, Kai wrote:
> > On Thu, 2024-01-18 at 18:01 +0200, Nikolay Borisov wrote:
> > > TDX doesn't currently support kexec so disable the latter when TDX
> > > is detected at boot time. If kexec must absolutely be supported then
> > > TDX can be disabled from the bios.
> > > 
> > > Making this decision at run time rather than as a compile time option
> > > allows distribution kernels to have both enabled and delegate to the
> > > user whether they want to use TDX/Kexec.
> > > 
> > > Signed-off-by: Nikolay Borisov <nik.borisov@suse.com>
> > 
> > Hi Nikolay,
> > 
> > Thanks for the patch.
> > 
> > I am working in progress on patches to make kexec() work with TDX.  I plan to
> > send them out soon (e.g., next week), but I think perhaps your patch is
> > reasonable before that is merged.
> 
> I thought Kirill's series rectifies this ?
> 

No that's for TDX guest.
  

On 19.01.24 г. 2:52 ч., Huang, Kai wrote:
> On Fri, 2024-01-19 at 02:49 +0200, Nikolay Borisov wrote:
>> [Adding Kirill as he has a series in flight about KEXEC]
>>
>> On 18.01.24 г. 23:31 ч., Huang, Kai wrote:
>>> On Thu, 2024-01-18 at 18:01 +0200, Nikolay Borisov wrote:
>>>> TDX doesn't currently support kexec so disable the latter when TDX
>>>> is detected at boot time. If kexec must absolutely be supported then
>>>> TDX can be disabled from the bios.
>>>>
>>>> Making this decision at run time rather than as a compile time option
>>>> allows distribution kernels to have both enabled and delegate to the
>>>> user whether they want to use TDX/Kexec.
>>>>
>>>> Signed-off-by: Nikolay Borisov <nik.borisov@suse.com>
>>>
>>> Hi Nikolay,
>>>
>>> Thanks for the patch.
>>>
>>> I am working in progress on patches to make kexec() work with TDX.  I plan to
>>> send them out soon (e.g., next week), but I think perhaps your patch is
>>> reasonable before that is merged.
>>
>> I thought Kirill's series rectifies this ?
>>
> 
> No that's for TDX guest.

Well in this case shouldn't INTEL_TDX_GUEST also be gated on KEXEC_CORE 
being inoperable either via Kconfig option or via a similar approach to 
this one (if it's accepted)?