linux-kernel - Re: [PATCH Part2 RFC v2 32/37] KVM: SVM: Add support to handle MSR based Page State Change VMGEXIT

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Date:   Mon, 10 May 2021 12:51:36 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Peter Gonda <pgonda@...gle.com>
Cc:     brijesh.singh@....com, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm list <kvm@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, jroedel@...e.de,
        "Lendacky, Thomas" <thomas.lendacky@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>,
        David Rientjes <rientjes@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>, peterz@...radead.org,
        "H. Peter Anvin" <hpa@...or.com>, tony.luck@...el.com
Subject: Re: [PATCH Part2 RFC v2 32/37] KVM: SVM: Add support to handle MSR
 based Page State Change VMGEXIT

Hi Peter,

On 5/10/21 12:30 PM, Peter Gonda wrote:
>> +static int snp_make_page_shared(struct kvm_vcpu *vcpu, gpa_t gpa, kvm_pfn_t pfn, int level)
>> +{
>> +       struct rmpupdate val;
>> +       int rc, rmp_level;
>> +       struct rmpentry *e;
>> +
>> +       e = snp_lookup_page_in_rmptable(pfn_to_page(pfn), &rmp_level);
>> +       if (!e)
>> +               return -EINVAL;
>> +
>> +       if (!rmpentry_assigned(e))
>> +               return 0;
>> +
>> +       /* Log if the entry is validated */
>> +       if (rmpentry_validated(e))
>> +               pr_debug_ratelimited("Remove RMP entry for a validated gpa 0x%llx\n", gpa);
>> +
>> +       /*
>> +        * Is the page part of an existing 2M RMP entry ? Split the 2MB into multiple
>> +        * of 4K-page before making the memory shared.
>> +        */
>> +       if ((level == PG_LEVEL_4K) && (rmp_level == PG_LEVEL_2M)) {
>> +               rc = snp_rmptable_psmash(vcpu, pfn);
>> +               if (rc)
>> +                       return rc;
>> +       }
>> +
>> +       memset(&val, 0, sizeof(val));
>> +       val.pagesize = X86_TO_RMP_PG_LEVEL(level);
> This is slightly different from Rev 2.00 of the GHCB spec. This
> defaults to 2MB page sizes, when the spec says the only valid settings
> for level are 0 -> 4k pages or 1 -> 2MB pages. Should this enforce the
> same strictness as the spec?


The caller of the snp_make_page_shared() must pass the x86 page level.
We should reach here after all the guest provide value have passed
through checks.

The call sequence in this case should be:

snp_handle_vmgexit_msr_protocol()

 __snp_handle_page_state_change(vcpu, gfn_to_gpa(gfn), PG_LEVEL_4K)

  snp_make_page_shared(..., level)

Am I missing something  ?

>> +       return rmpupdate(pfn_to_page(pfn), &val);
>> +}
>> +
>> +static int snp_make_page_private(struct kvm_vcpu *vcpu, gpa_t gpa, kvm_pfn_t pfn, int level)
>> +{
>> +       struct kvm_sev_info *sev = &to_kvm_svm(vcpu->kvm)->sev_info;
>> +       struct rmpupdate val;
>> +       struct rmpentry *e;
>> +       int rmp_level;
>> +
>> +       e = snp_lookup_page_in_rmptable(pfn_to_page(pfn), &rmp_level);
>> +       if (!e)
>> +               return -EINVAL;
>> +
>> +       /* Log if the entry is validated */
>> +       if (rmpentry_validated(e))
>> +               pr_err_ratelimited("Asked to make a pre-validated gpa %llx private\n", gpa);
>> +
>> +       memset(&val, 0, sizeof(val));
>> +       val.gpa = gpa;
>> +       val.asid = sev->asid;
>> +       val.pagesize = X86_TO_RMP_PG_LEVEL(level);
> Same comment as above.

See my above response.


>
>> +       val.assigned = true;
>> +
>> +       return rmpupdate(pfn_to_page(pfn), &val);
>> +}