Re: [PATCH v2 15/25] x86/sev: Introduce snp leaked pages list

Borislav Petkov
2024-01-29T14:30:26Z

On Mon, Jan 29, 2024 at 03:26:29PM +0100, Vlastimil Babka wrote:
> Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
>
> Some minor nitpicks:

Thanks, here's what I have applied:

commit c3875aff4e0739a6af385795470da70d675a7635
Author: Ashish Kalra <ashish.kalra@amd.com>
Date: Thu Jan 25 22:11:15 2024 -0600

x86/sev: Introduce an SNP leaked pages list

Pages are unsafe to be released back to the page-allocator if they
have been transitioned to firmware/guest state and can't be reclaimed
or transitioned back to hypervisor/shared state. In this case, add them
to an internal leaked pages list to ensure that they are not freed or
touched/accessed to cause fatal page faults.

[ mdr: Relocate to arch/x86/virt/svm/sev.c ]

Suggested-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Link: https://lore.kernel.org/r/20240126041126.1927228-16-michael.roth@amd.com

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index d3ccb7a0c7e9..435ba9bc4510 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -264,6 +264,7 @@ void snp_dump_hva_rmpentry(unsigned long address);
int psmash(u64 pfn);
int rmp_make_private(u64 pfn, u64 gpa, enum pg_level level, int asid, bool immutable);
int rmp_make_shared(u64 pfn, enum pg_level level);
+void snp_leak_pages(u64 pfn, unsigned int npages);
#else
static inline bool snp_probe_rmptable_info(void) { return false; }
static inline int snp_lookup_rmpentry(u64 pfn, bool *assigned, int *level) { return -ENODEV; }
@@ -275,6 +276,7 @@ static inline int rmp_make_private(u64 pfn, u64 gpa, enum pg_level level, int as
return -ENODEV;
}
static inline int rmp_make_shared(u64 pfn, enum pg_level level) { return -ENODEV; }
+static inline void snp_leak_pages(u64 pfn, unsigned int npages) {}
#endif

#endif
diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
index f1be56555ee6..901863a842d7 100644
--- a/arch/x86/virt/svm/sev.c
+++ b/arch/x86/virt/svm/sev.c
@@ -65,6 +65,11 @@ static u64 probed_rmp_base, probed_rmp_size;
static struct rmpentry *rmptable __ro_after_init;
static u64 rmptable_max_pfn __ro_after_init;

+static LIST_HEAD(snp_leaked_pages_list);
+static DEFINE_SPINLOCK(snp_leaked_pages_list_lock);
+
+static unsigned long snp_nr_leaked_pages;
+
#undef pr_fmt
#define pr_fmt(fmt) "SEV-SNP: " fmt

@@ -515,3 +520,35 @@ int rmp_make_shared(u64 pfn, enum pg_level level)
return rmpupdate(pfn, &state);
}
EXPORT_SYMBOL_GPL(rmp_make_shared);
+
+void snp_leak_pages(u64 pfn, unsigned int npages)
+{
+ struct page *page = pfn_to_page(pfn);
+
+ pr_warn("Leaking PFN range 0x%llx-0x%llx\n", pfn, pfn + npages);
+
+ spin_lock(&snp_leaked_pages_list_lock);
+ while (npages--) {
+
+ /*
+ * Reuse the page's buddy list for chaining into the leaked
+ * pages list. This page should not be on a free list currently
+ * and is also unsafe to be added to a free list.
+ */
+ if (likely(!PageCompound(page)) ||
+
+ /*
+ * Skip inserting tail pages of compound page as
+ * page->buddy_list of tail pages is not usable.
+ */
+ (PageHead(page) && compound_nr(page) <= npages))
+ list_add_tail(&page->buddy_list, &snp_leaked_pages_list);
+
+ dump_rmpentry(pfn);
+ snp_nr_leaked_pages++;
+ pfn++;
+ page++;
+ }
+ spin_unlock(&snp_leaked_pages_list_lock);
+}
+EXPORT_SYMBOL_GPL(snp_leak_pages);

--
Regards/Gruss,
Boris.