linux-kernel - Re: [RFC Part2 PATCH 06/30] x86/fault: dump the RMP entry on #PF

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Date:   Wed, 24 Mar 2021 15:35:20 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     brijesh.singh@....com, LKML <linux-kernel@...r.kernel.org>,
        X86 ML <x86@...nel.org>, kvm list <kvm@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Joerg Roedel <jroedel@...e.de>,
        "H. Peter Anvin" <hpa@...or.com>, Tony Luck <tony.luck@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        David Rientjes <rientjes@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC Part2 PATCH 06/30] x86/fault: dump the RMP entry on #PF


On 3/24/21 12:47 PM, Andy Lutomirski wrote:
> On Wed, Mar 24, 2021 at 10:04 AM Brijesh Singh <brijesh.singh@....com> wrote:
>> 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 <tglx@...utronix.de>
>> Cc: Ingo Molnar <mingo@...hat.com>
>> Cc: Borislav Petkov <bp@...en8.de>
>> Cc: Joerg Roedel <jroedel@...e.de>
>> Cc: "H. Peter Anvin" <hpa@...or.com>
>> Cc: Tony Luck <tony.luck@...el.com>
>> Cc: Dave Hansen <dave.hansen@...el.com>
>> Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>
>> Cc: Paolo Bonzini <pbonzini@...hat.com>
>> Cc: Tom Lendacky <thomas.lendacky@....com>
>> Cc: David Rientjes <rientjes@...gle.com>
>> Cc: Sean Christopherson <seanjc@...gle.com>
>> Cc: x86@...nel.org
>> Cc: kvm@...r.kernel.org
>> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
>> ---
>>  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.