On 3/24/21 12:47 PM, Andy Lutomirski wrote:

On Wed, Mar 24, 2021 at 10:04 AM Brijesh Singh [off-list ref] wrote:

quoted

If hardware detects an RMP violation, it will raise a page-fault exception
with the RMP bit set. To help the debug, dump the RMP entry of the faulting
address.

Cc: Thomas Gleixner <redacted>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Joerg Roedel <redacted>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Dave Hansen <redacted>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: x86@kernel.org
Cc: kvm@vger.kernel.org
Signed-off-by: Brijesh Singh <redacted>
---
 arch/x86/mm/fault.c | 75 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index f39b551f89a6..7605e06a6dd9 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c

@@ -31,6 +31,7 @@
 #include <asm/pgtable_areas.h>         /* VMALLOC_START, ...           */
 #include <asm/kvm_para.h>              /* kvm_handle_async_pf          */
 #include <asm/vdso.h>                  /* fixup_vdso_exception()       */
+#include <asm/sev-snp.h>               /* lookup_rmpentry ...          */

 #define CREATE_TRACE_POINTS
 #include <asm/trace/exceptions.h>

@@ -147,6 +148,76 @@ is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr)
 DEFINE_SPINLOCK(pgd_lock);
 LIST_HEAD(pgd_list);

+static void dump_rmpentry(struct page *page, rmpentry_t *e)
+{
+       unsigned long paddr = page_to_pfn(page) << PAGE_SHIFT;
+
+       pr_alert("RMPEntry paddr 0x%lx [assigned=%d immutable=%d pagesize=%d gpa=0x%lx asid=%d "
+               "vmsa=%d validated=%d]\n", paddr, rmpentry_assigned(e), rmpentry_immutable(e),
+               rmpentry_pagesize(e), rmpentry_gpa(e), rmpentry_asid(e), rmpentry_vmsa(e),
+               rmpentry_validated(e));
+       pr_alert("RMPEntry paddr 0x%lx %016llx %016llx\n", paddr, e->high, e->low);
+}
+
+static void show_rmpentry(unsigned long address)
+{
+       struct page *page = virt_to_page(address);

This is an error path, and I don't think you have any particular
guarantee that virt_to_page(address) is valid.  Please add appropriate
validation or use one of the slow lookup helpers.

Noted, thanks for the quick feedback.