Re: [PATCH Part2 v6 10/49] x86/fault: Add support to dump RMP entry on fault

Jeremi Piotrowski
2022-06-22T14:33:49Z

On Mon, Jun 20, 2022 at 11:03:58PM +0000, Ashish Kalra wrote:
> From: Brijesh Singh <brijesh.singh@amd.com>
>
> 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 <brijesh.singh@amd.com>
> ---
> 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)
>
> #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
>
> #endif
> diff --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)
> +{
> + unsigned long pfn_end;
> + struct rmpentry *e;
> + int level;
> +
> + e = __snp_lookup_rmpentry(pfn, &level);
> + if (!e) {

__snp_lookup_rmpentry may return -errno so this should be:

if (e != 1)

> + pr_alert("failed to read RMP entry pfn 0x%llx\n", pfn);
> + 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 not
> + * 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)

if (e != 1)

> + return;
> +
> + if (e->low || e->high)
> + pr_alert("RMPEntry paddr 0x%llx: [high=0x%016llx low=0x%016llx]\n",
> + pfn << PAGE_SHIFT, e->high, e->low);
> + pfn++;
> + }
> +}
> +EXPORT_SYMBOL_GPL(dump_rmpentry);
> +
> /*
> * Return 1 if the RMP entry is assigned, 0 if it exists but is not assigned,
> * and -errno if there is no corresponding RMP entry.
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index f5de9673093a..25896a6ba04a 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -34,6 +34,7 @@
> #include <asm/kvm_para.h> /* kvm_handle_async_pf */
> #include <asm/vdso.h> /* fixup_vdso_exception() */
> #include <asm/irq_stack.h>
> +#include <asm/sev.h> /* dump_rmpentry() */
>
> #define CREATE_TRACE_POINTS
> #include <asm/trace/exceptions.h>
> @@ -290,7 +291,7 @@ static bool low_pfn(unsigned long pfn)
> return pfn < max_low_pfn;
> }
>
> -static void dump_pagetable(unsigned long address)
> +static void dump_pagetable(unsigned long address, bool show_rmpentry)
> {
> pgd_t *base = __va(read_cr3_pa());
> pgd_t *pgd = &base[pgd_index(address)];
> @@ -346,10 +347,11 @@ static int bad_address(void *p)
> return get_kernel_nofault(dummy, (unsigned long *)p);
> }
>
> -static void dump_pagetable(unsigned long address)
> +static void dump_pagetable(unsigned long address, bool show_rmpentry)
> {
> pgd_t *base = __va(read_cr3_pa());
> pgd_t *pgd = base + pgd_index(address);
> + unsigned long pfn;
> p4d_t *p4d;
> pud_t *pud;
> pmd_t *pmd;
> @@ -367,6 +369,7 @@ static void dump_pagetable(unsigned long address)
> if (bad_address(p4d))
> goto bad;
>
> + pfn = p4d_pfn(*p4d);
> pr_cont("P4D %lx ", p4d_val(*p4d));
> if (!p4d_present(*p4d) || p4d_large(*p4d))
> goto out;
> @@ -375,6 +378,7 @@ static void dump_pagetable(unsigned long address)
> if (bad_address(pud))
> goto bad;
>
> + pfn = pud_pfn(*pud);
> pr_cont("PUD %lx ", pud_val(*pud));
> if (!pud_present(*pud) || pud_large(*pud))
> goto out;
> @@ -383,6 +387,7 @@ static void dump_pagetable(unsigned long address)
> if (bad_address(pmd))
> goto bad;
>
> + pfn = pmd_pfn(*pmd);
> pr_cont("PMD %lx ", pmd_val(*pmd));
> if (!pmd_present(*pmd) || pmd_large(*pmd))
> goto out;
> @@ -391,9 +396,13 @@ static void dump_pagetable(unsigned long address)
> if (bad_address(pte))
> goto bad;
>
> + pfn = pte_pfn(*pte);
> pr_cont("PTE %lx", pte_val(*pte));
> out:
> pr_cont("\n");
> +
> + if (show_rmpentry)
> + dump_rmpentry(pfn);
> return;
> bad:
> pr_info("BAD\n");
> @@ -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);
> }
>
> static noinline void
> @@ -596,7 +605,7 @@ pgtable_bad(struct pt_regs *regs, unsigned long error_code,
>
> printk(KERN_ALERT "%s: Corrupted page table at address %lx\n",
> tsk->comm, address);
> - dump_pagetable(address);
> + dump_pagetable(address, false);
>
> if (__die("Bad pagetable", regs, error_code))
> sig = 0;
> diff --git a/include/linux/sev.h b/include/linux/sev.h
> index 1a68842789e1..734b13a69c54 100644
> --- a/include/linux/sev.h
> +++ b/include/linux/sev.h
> @@ -16,6 +16,7 @@ int snp_lookup_rmpentry(u64 pfn, int *level);
> 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 dump_rmpentry(u64 pfn);
> #else
> static inline int snp_lookup_rmpentry(u64 pfn, int *level) { return 0; }
> static inline int psmash(u64 pfn) { return -ENXIO; }
> @@ -25,6 +26,7 @@ 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 dump_rmpentry(u64 pfn) { }
>
> #endif /* CONFIG_AMD_MEM_ENCRYPT */
> #endif /* __LINUX_SEV_H */
> --
> 2.25.1
>