Re: [PATCH Part2 v6 10/49] x86/fault: Add support to dump RMP entry on fault
From: Borislav Petkov <bp@alien8.de>
Date: 2022-08-23 16:53:49
Also in:
kvm, linux-crypto, linux-mm, lkml
On Mon, Jun 20, 2022 at 11:03:58PM +0000, Ashish Kalra wrote:
quoted hunk ↗ jump to hunk
From: Brijesh Singh <redacted> When SEV-SNP is enabled globally, a write from the host goes through the RMP check. If the hardware encounters the check failure, then it raises the #PF (with RMP set). Dump the RMP entry at the faulting pfn to help the debug. Signed-off-by: Brijesh Singh <redacted> --- arch/x86/include/asm/sev.h | 7 +++++++ arch/x86/kernel/sev.c | 43 ++++++++++++++++++++++++++++++++++++++ arch/x86/mm/fault.c | 17 +++++++++++---- include/linux/sev.h | 2 ++ 4 files changed, 65 insertions(+), 4 deletions(-)diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h index 6ab872311544..c0c4df817159 100644 --- a/arch/x86/include/asm/sev.h +++ b/arch/x86/include/asm/sev.h@@ -113,6 +113,11 @@ struct __packed rmpentry { #define rmpentry_assigned(x) ((x)->info.assigned) #define rmpentry_pagesize(x) ((x)->info.pagesize) +#define rmpentry_vmsa(x) ((x)->info.vmsa) +#define rmpentry_asid(x) ((x)->info.asid) +#define rmpentry_validated(x) ((x)->info.validated) +#define rmpentry_gpa(x) ((unsigned long)(x)->info.gpa) +#define rmpentry_immutable(x) ((x)->info.immutable)
If you're going to do that, use inline functions pls so that it checks the argument at least. Also, add such functions only when they're called multiple times - no need to add one for every field if you're going to access that field only once in the whole kernel.
quoted hunk ↗ jump to hunk
#define RMPADJUST_VMSA_PAGE_BIT BIT(16)@@ -205,6 +210,7 @@ void snp_set_wakeup_secondary_cpu(void); bool snp_init(struct boot_params *bp); void snp_abort(void); int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, unsigned long *fw_err); +void dump_rmpentry(u64 pfn); #else static inline void sev_es_ist_enter(struct pt_regs *regs) { } static inline void sev_es_ist_exit(void) { }@@ -229,6 +235,7 @@ static inline int snp_issue_guest_request(u64 exit_code, struct snp_req_data *in { return -ENOTTY; } +static inline void dump_rmpentry(u64 pfn) {} #endif #endifdiff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c index 734cddd837f5..6640a639fffc 100644 --- a/arch/x86/kernel/sev.c +++ b/arch/x86/kernel/sev.c@@ -2414,6 +2414,49 @@ static struct rmpentry *__snp_lookup_rmpentry(u64 pfn, int *level) return entry; } +void dump_rmpentry(u64 pfn)
External function - it better belong to a namespace: sev_dump_rmpentry()
+{
+ unsigned long pfn_end;
+ struct rmpentry *e;
+ int level;
+
+ e = __snp_lookup_rmpentry(pfn, &level);
+ if (!e) {
+ pr_alert("failed to read RMP entry pfn 0x%llx\n", pfn);Why alert? Dumping stuff is either pr_debug or pr_info...
+ return;
+ }
+
+ if (rmpentry_assigned(e)) {
+ pr_alert("RMPEntry paddr 0x%llx [assigned=%d immutable=%d pagesize=%d gpa=0x%lx"
+ " asid=%d vmsa=%d validated=%d]\n", pfn << PAGE_SHIFT,
+ rmpentry_assigned(e), rmpentry_immutable(e), rmpentry_pagesize(e),
+ rmpentry_gpa(e), rmpentry_asid(e), rmpentry_vmsa(e),
+ rmpentry_validated(e));
+ return;
+ }
+
+ /*
+ * If the RMP entry at the faulting pfn was not assigned, then we do notWho's "we"?
+ * know what caused the RMP violation. To get some useful debug information,
+ * let iterate through the entire 2MB region, and dump the RMP entries if
+ * one of the bit in the RMP entry is set.
+ */
+ pfn = pfn & ~(PTRS_PER_PMD - 1);
+ pfn_end = pfn + PTRS_PER_PMD;
+
+ while (pfn < pfn_end) {
+ e = __snp_lookup_rmpentry(pfn, &level);
+ if (!e)
+ return;
+
+ if (e->low || e->high)This is going to confuse people because they're going to miss a zero entry. Just dump the whole thing. ...
quoted hunk ↗ jump to hunk
@@ -579,7 +588,7 @@ show_fault_oops(struct pt_regs *regs, unsigned long error_code, unsigned long ad show_ldttss(&gdt, "TR", tr); } - dump_pagetable(address); + dump_pagetable(address, error_code & X86_PF_RMP);
Eww.
I'd prefer to see
pfn = dump_pagetable(address);
if (error_code & X86_PF_RMP)
sev_dump_rmpentry(pfn);
instead of passing around this SEV-specific arg in generic x86 fault code.
The change to return the pfn from dump_pagetable() should be a pre-patch ofc.
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette