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

[Jeremi Piotrowski]

On Wed, Jun 22, 2022 at 04:33:04PM +0200, Jeremi Piotrowski wrote:
> On Mon, Jun 20, 2022 at 11:03:58PM +0000, Ashish Kalra wrote:
> > From: Brijesh Singh <brijesh.singh@xxxxxxx>
> > 
> > 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@xxxxxxx>
> > ---
> >  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)

Sorry, actually it should be:

  if (IS_ERR_OR_NULL(e)) {

> 
> > +		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)
> 

and this too:

  if (IS_ERR_OR_NULL(e))


> > +			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
> >