Re: [PATCH v15 17/23] x86/kexec: Flush cache of TDX private memory

Dave Hansen
2023-11-27T18:13:47Z

On 11/9/23 03:55, Kai Huang wrote:
...
> --- a/arch/x86/kernel/reboot.c
> +++ b/arch/x86/kernel/reboot.c
> @@ -31,6 +31,7 @@
> #include <asm/realmode.h>
> #include <asm/x86_init.h>
> #include <asm/efi.h>
> +#include <asm/tdx.h>
>
> /*
> * Power off function, if any
> @@ -741,6 +742,20 @@ void native_machine_shutdown(void)
> local_irq_disable();
> stop_other_cpus();
> #endif
> + /*
> + * stop_other_cpus() has flushed all dirty cachelines of TDX
> + * private memory on remote cpus. Unlike SME, which does the
> + * cache flush on _this_ cpu in the relocate_kernel(), flush
> + * the cache for _this_ cpu here. This is because on the
> + * platforms with "partial write machine check" erratum the
> + * kernel needs to convert all TDX private pages back to normal
> + * before booting to the new kernel in kexec(), and the cache
> + * flush must be done before that. If the kernel took SME's way,
> + * it would have to muck with the relocate_kernel() assembly to
> + * do memory conversion.
> + */
> + if (platform_tdx_enabled())
> + native_wbinvd();

Why can't the TDX host code just set host_mem_enc_active=1?

Sure, you'll end up *using* the SME WBINVD support, but then you don't
have two different WBINVD call sites. You also don't have to mess with
a single line of assembly.