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

Dave Hansen
2023-11-27T21:06:15Z

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On 11/27/23 12:52, Huang, Kai wrote:
> --- a/arch/x86/kernel/machine_kexec_64.c
> +++ b/arch/x86/kernel/machine_kexec_64.c
> @@ -377,7 +377,8 @@ void machine_kexec(struct kimage *image)
> (unsigned long)page_list,
> image->start,
> image->preserve_context,
> -
> cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT));
> + cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT)
> ||
> + platform_tdx_enabled());

Well, something more like the attached would be preferable, but you've
got the right idea logically.

[-- Attachment #2: cc-host-mem-incoherent.patch --]
[-- Type: text/x-patch, Size: 2319 bytes --]

---

b/arch/x86/coco/core.c | 1 +
b/arch/x86/kernel/machine_kexec_64.c | 2 +-
b/include/linux/cc_platform.h | 16 ++++++++++++++++
3 files changed, 18 insertions(+), 1 deletion(-)

diff -puN include/linux/cc_platform.h~cc-host-mem-incoherent include/linux/cc_platform.h
--- a/include/linux/cc_platform.h~cc-host-mem-incoherent 2023-11-27 12:20:44.217381008 -0800
+++ b/include/linux/cc_platform.h 2023-11-27 12:25:05.771073193 -0800
@@ -43,6 +43,22 @@ enum cc_attr {
CC_ATTR_HOST_MEM_ENCRYPT,

/**
+ * @CC_ATTR_HOST_MEM_INCOHERENT: Host memory encryption can be
+ * incoherent
+ *
+ * The platform/OS is running as a bare-metal system or a hypervisor.
+ * The memory encryption engine might have left non-cache-coherent
+ * data in the caches that needs to be flushed.
+ *
+ * Use this in places where the cache coherency of the memory matters
+ * but the encryption status does not.
+ *
+ * Includes all systems that set CC_ATTR_HOST_MEM_ENCRYPT, but
+ * aditionally adds TDX hosts.
+ */
+ CC_ATTR_HOST_MEM_INCOHERENT,
+
+ /**
* @CC_ATTR_GUEST_MEM_ENCRYPT: Guest memory encryption is active
*
* The platform/OS is running as a guest/virtual machine and actively
diff -puN arch/x86/kernel/machine_kexec_64.c~cc-host-mem-incoherent arch/x86/kernel/machine_kexec_64.c
--- a/arch/x86/kernel/machine_kexec_64.c~cc-host-mem-incoherent 2023-11-27 12:25:13.527115260 -0800
+++ b/arch/x86/kernel/machine_kexec_64.c 2023-11-27 13:04:19.732959001 -0800
@@ -361,7 +361,7 @@ void machine_kexec(struct kimage *image)
(unsigned long)page_list,
image->start,
image->preserve_context,
- cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT));
+ cc_platform_has(CC_ATTR_HOST_MEM_INCOHERENT));

#ifdef CONFIG_KEXEC_JUMP
if (image->preserve_context)
diff -puN arch/x86/coco/core.c~cc-host-mem-incoherent arch/x86/coco/core.c
--- a/arch/x86/coco/core.c~cc-host-mem-incoherent 2023-11-27 12:26:02.535372377 -0800
+++ b/arch/x86/coco/core.c 2023-11-27 12:26:12.371422241 -0800
@@ -70,6 +70,7 @@ static bool noinstr amd_cc_platform_has(
return sme_me_mask;

case CC_ATTR_HOST_MEM_ENCRYPT:
+ case CC_ATTR_HOST_MEM_INCOHERENT:
return sme_me_mask && !(sev_status & MSR_AMD64_SEV_ENABLED);

case CC_ATTR_GUEST_MEM_ENCRYPT:
_