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

[Nikolay Borisov]

[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@xxxxxxxx>
>
> 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@xxxxxxxxx>
>
> > ---
> >
> > 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