The kernel will convert all shared memory back to private during kexec.
The direct mapping page tables will provide information on which memory
is shared.
It is extremely important to convert all shared memory. If a page is
missed, it will cause the second kernel to crash when it accesses it.
Keep track of the number of shared pages. This will allow for
cross-checking against the shared information in the direct mapping and
reporting if the shared bit is lost.
Signed-off-by: Kirill A. Shutemov <[email protected]>
---
arch/x86/coco/tdx/tdx.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 26fa47db5782..979891e97d83 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -38,6 +38,8 @@
#define TDREPORT_SUBTYPE_0 0
+static atomic_long_t nr_shared;
+
/* Called from __tdx_hypercall() for unrecoverable failure */
noinstr void __noreturn __tdx_hypercall_failed(void)
{
@@ -821,6 +823,11 @@ static int tdx_enc_status_change_finish(unsigned long vaddr, int numpages,
if (!enc && !tdx_enc_status_changed(vaddr, numpages, enc))
return -EIO;
+ if (enc)
+ atomic_long_sub(numpages, &nr_shared);
+ else
+ atomic_long_add(numpages, &nr_shared);
+
return 0;
}
--
2.43.0
On 3/25/24 3:39 AM, Kirill A. Shutemov wrote:
> The kernel will convert all shared memory back to private during kexec.
> The direct mapping page tables will provide information on which memory
> is shared.
>
> It is extremely important to convert all shared memory. If a page is
> missed, it will cause the second kernel to crash when it accesses it.
>
> Keep track of the number of shared pages. This will allow for
> cross-checking against the shared information in the direct mapping and
> reporting if the shared bit is lost.
>
> Signed-off-by: Kirill A. Shutemov <[email protected]>
> ---
Looks good to me.
Reviewed-by: Kuppuswamy Sathyanarayanan <[email protected]>
> arch/x86/coco/tdx/tdx.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
> index 26fa47db5782..979891e97d83 100644
> --- a/arch/x86/coco/tdx/tdx.c
> +++ b/arch/x86/coco/tdx/tdx.c
> @@ -38,6 +38,8 @@
>
> #define TDREPORT_SUBTYPE_0 0
>
> +static atomic_long_t nr_shared;
> +
> /* Called from __tdx_hypercall() for unrecoverable failure */
> noinstr void __noreturn __tdx_hypercall_failed(void)
> {
> @@ -821,6 +823,11 @@ static int tdx_enc_status_change_finish(unsigned long vaddr, int numpages,
> if (!enc && !tdx_enc_status_changed(vaddr, numpages, enc))
> return -EIO;
>
> + if (enc)
> + atomic_long_sub(numpages, &nr_shared);
> + else
> + atomic_long_add(numpages, &nr_shared);
> +
> return 0;
> }
>
--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer
On Mon, 2024-03-25 at 12:39 +0200, Kirill A. Shutemov wrote:
> The kernel will convert all shared memory back to private during kexec.
> The direct mapping page tables will provide information on which memory
> is shared.
>
> It is extremely important to convert all shared memory. If a page is
> missed, it will cause the second kernel to crash when it accesses it.
>
> Keep track of the number of shared pages. This will allow for
> cross-checking against the shared information in the direct mapping and
> reporting if the shared bit is lost.
>
> Signed-off-by: Kirill A. Shutemov <[email protected]>
> ---
>
Reviewed-by: Kai Huang <[email protected]>