linux-kernel - Re: [PATCH v3 51/75] x86/sev-es: Handle MMIO events

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Date:   Thu, 11 Jun 2020 14:40:08 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     x86@...nel.org, hpa@...or.com, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Jiri Slaby <jslaby@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        David Rientjes <rientjes@...gle.com>,
        Cfir Cohen <cfir@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mike Stunes <mstunes@...are.com>,
        Joerg Roedel <jroedel@...e.de>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v3 51/75] x86/sev-es: Handle MMIO events

On Tue, May 19, 2020 at 11:32:02PM -0700, Sean Christopherson wrote:
> '0' is a valid physical address.  It happens to be reserved in the kernel
> thanks to L1TF, but using '0' as an error code is ugly.  Not to mention
> none of the callers actually check the result.

Right, I changed the function to better handle error cases and added
checks to the call-sites. It looks like below now:

static bool vc_slow_virt_to_phys(struct ghcb *ghcb, struct es_em_ctxt *ctxt,
                                 unsigned long vaddr, phys_addr_t *paddr)
{
        unsigned long va = (unsigned long)vaddr;
        unsigned int level;
        phys_addr_t pa;
        pgd_t *pgd;
        pte_t *pte;

        pgd = pgd_offset(current->active_mm, va);
        pte = lookup_address_in_pgd(pgd, va, &level);
        if (!pte) {
                ctxt->fi.vector     = X86_TRAP_PF;
                ctxt->fi.cr2        = vaddr;
                ctxt->fi.error_code = 0;

                if (user_mode(ctxt->regs))
                        ctxt->fi.error_code |= X86_PF_USER;

                return false;
        }

        pa = (phys_addr_t)pte_pfn(*pte) << PAGE_SHIFT;
        pa |= va & ~page_level_mask(level);

        *paddr = pa;

        return true;
}