On Thu, Jun 26, 2025 at 10:48:47PM +1200, Kai Huang wrote:
...
> Doing WBINVD in stop_this_cpu() could potentially increase the chance to
> trigger the above "race" despite it's still rare to happen.
Oh the amount of text...
Please run it and all your comments through AI to simplify formulations etc.
It is a lot to read.
> Signed-off-by: Kai Huang <kai.huang@xxxxxxxxx>
> ---
> arch/x86/include/asm/kexec.h | 2 +-
> arch/x86/include/asm/processor.h | 2 ++
> arch/x86/kernel/cpu/amd.c | 16 ++++++++++++++++
> arch/x86/kernel/machine_kexec_64.c | 15 ++++++++++-----
> arch/x86/kernel/process.c | 16 +++-------------
> arch/x86/kernel/relocate_kernel_64.S | 15 +++++++++++----
> 6 files changed, 43 insertions(+), 23 deletions(-)
>
> diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
> index f2ad77929d6e..d7e93522b93d 100644
> --- a/arch/x86/include/asm/kexec.h
> +++ b/arch/x86/include/asm/kexec.h
> @@ -122,7 +122,7 @@ relocate_kernel_fn(unsigned long indirection_page,
> unsigned long pa_control_page,
> unsigned long start_address,
> unsigned int preserve_context,
> - unsigned int host_mem_enc_active);
> + unsigned int cache_incoherent);
So preserve_context and cache_incoherent are both a *single* bit of
information. And we use two u32s for that?!?!
How about flags please?
> #endif
> extern relocate_kernel_fn relocate_kernel;
> #define ARCH_HAS_KIMAGE_ARCH
> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index bde58f6510ac..a24c7805acdb 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -731,6 +731,8 @@ void __noreturn stop_this_cpu(void *dummy);
> void microcode_check(struct cpuinfo_x86 *prev_info);
> void store_cpu_caps(struct cpuinfo_x86 *info);
>
So much text above - not a single comment here explaining what this var is
for.
> +DECLARE_PER_CPU(bool, cache_state_incoherent);
> +
> enum l1tf_mitigations {
> L1TF_MITIGATION_OFF,
> L1TF_MITIGATION_AUTO,
> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> index f18f540db58c..4c7fde344216 100644
> --- a/arch/x86/kernel/cpu/amd.c
> +++ b/arch/x86/kernel/cpu/amd.c
> @@ -503,6 +503,22 @@ static void early_detect_mem_encrypt(struct cpuinfo_x86 *c)
> {
> u64 msr;
>
> + /*
> + * Mark using wbinvd is needed during kexec on processors that
For all text: write insns in caps pls - WBINVD.
> + * support SME. This provides support for performing a successful
> + * kexec when going from SME inactive to SME active (or vice-versa).
> + *
> + * The cache must be cleared so that if there are entries with the
> + * same physical address, both with and without the encryption bit,
> + * they don't race each other when flushed and potentially end up
> + * with the wrong entry being committed to memory.
> + *
> + * Test the CPUID bit directly because the machine might've cleared
> + * X86_FEATURE_SME due to cmdline options.
Where?
That same function does the clearing later...
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
