From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-il1-f182.google.com (mail-il1-f182.google.com [209.85.166.182]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 179356AA2 for ; Mon, 19 Sep 2022 17:54:02 +0000 (UTC) Received: by mail-il1-f182.google.com with SMTP id g6so35710ild.6 for ; Mon, 19 Sep 2022 10:54:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date; bh=/cf7B/KTsLD75IcdMZipBXm6ofpyaTAcEkMwbp5iR00=; b=R8mhDvftQzWNGK0iyvTa9nSIWZrFtnkIInr7JSr2ggsBoL0OTaAAJ8tWbpkuAvy5uz /KUqKCF6s6xS0GQg0bWo7WW2V5rhJSdcyvJdj3QJ8g7jcGbxnddmPgRlFFig95paopv9 JJitEjoyNVAtyNOz4042FtJmsLF6F0qY3daW/gDjQH/PduCqhXQvCb4a4wsPlcIyO9d2 OO/7Mv1YzGbaTOiX3ImsaQ+5viwPfIzfyLecupDW8Q+rHJrno580i7K6KH0ODQsvfAYl 5W6sni6L8cuSeTVcAsYL23+NoDAUfHl1n82XX047aOmMYGSl7IPD6AXuHbyOys0rn2Ji ZM2Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date; bh=/cf7B/KTsLD75IcdMZipBXm6ofpyaTAcEkMwbp5iR00=; b=IttXSLpXVAQ7ATcmq7ORTPbTJiLFHM/JMN1PSxarMl+hizI0JBZa4a+ZnfIwnjKXGP JuzDXkakru/WaEuJobiHC8k8YM5LyNFsGvMmeiTZlmGznZ5fwSyp9tRpZ6FjP4W3Z3JL RO5tn+0HKEzFh2MPRESFuswptnAjcaRDNpusJFamdYkY87QWMcnKuW7Dgbal94CXngma wYQCOz7vLrDcwys8FuOGChO4VGTk3xIU/0pJSs9xekzRMbzarhOQmMzMXYF4QXfx9U/N kpMkhK9dgZW/bnOCmIL3G/hzYFVr+PVarEUbCOeSh6znfSV6e3nV54a5sodsqjyoaL90 bhQA== X-Gm-Message-State: ACrzQf0mqYXv23nKqst5whkLLqWSVF1o2UlZy8MB1dOF86lxNimJfXuB 2Lhn7oy233SAClsY26Ti7rayVyZo03meT94jOs368Q== X-Google-Smtp-Source: AMsMyM7ZwbCCz+Lnjmmlji90t5P++0wvHrAVUqDM1acb+Y9g6sLPifzlN/Q3k34EEoZMwTLsTTl3wGgSyLZbbRAEbkE= X-Received: by 2002:a92:ca49:0:b0:2f5:30:bfc1 with SMTP id q9-20020a92ca49000000b002f50030bfc1mr6478814ilo.224.1663610040996; Mon, 19 Sep 2022 10:54:00 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <78e30b5a25c926fcfdcaafea3d484f1bb25f20b9.1655761627.git.ashish.kalra@amd.com> In-Reply-To: From: Alper Gun Date: Mon, 19 Sep 2022 10:53:49 -0700 Message-ID: Subject: Re: [PATCH Part2 v6 37/49] KVM: SVM: Add support to handle MSR based Page State Change VMGEXIT To: Peter Gonda Cc: Ashish Kalra , "the arch/x86 maintainers" , LKML , kvm list , linux-coco@lists.linux.dev, Linux Memory Management List , Linux Crypto Mailing List , Thomas Gleixner , Ingo Molnar , Joerg Roedel , "Lendacky, Thomas" , "H. Peter Anvin" , Ard Biesheuvel , Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Jim Mattson , Andy Lutomirski , Dave Hansen , Sergio Lopez , Peter Zijlstra , Srinivas Pandruvada , David Rientjes , Dov Murik , Tobin Feldman-Fitzthum , Borislav Petkov , Michael Roth , Vlastimil Babka , "Kirill A . Shutemov" , Andi Kleen , Tony Luck , Marc Orr , Sathyanarayanan Kuppuswamy , "Dr. David Alan Gilbert" , jarkko@kernel.org Content-Type: text/plain; charset="UTF-8" On Fri, Aug 19, 2022 at 9:54 AM Peter Gonda wrote: > > > + > > +static int __snp_handle_page_state_change(struct kvm_vcpu *vcpu, enum psc_op op, gpa_t gpa, > > + int level) > > +{ > > + struct kvm_sev_info *sev = &to_kvm_svm(vcpu->kvm)->sev_info; > > + struct kvm *kvm = vcpu->kvm; > > + int rc, npt_level; > > + kvm_pfn_t pfn; > > + gpa_t gpa_end; > > + > > + gpa_end = gpa + page_level_size(level); > > + > > + while (gpa < gpa_end) { > > + /* > > + * If the gpa is not present in the NPT then build the NPT. > > + */ > > + rc = snp_check_and_build_npt(vcpu, gpa, level); > > + if (rc) > > + return -EINVAL; > > + > > + if (op == SNP_PAGE_STATE_PRIVATE) { > > + hva_t hva; > > + > > + if (snp_gpa_to_hva(kvm, gpa, &hva)) > > + return -EINVAL; > > + > > + /* > > + * Verify that the hva range is registered. This enforcement is > > + * required to avoid the cases where a page is marked private > > + * in the RMP table but never gets cleanup during the VM > > + * termination path. > > + */ > > + mutex_lock(&kvm->lock); > > + rc = is_hva_registered(kvm, hva, page_level_size(level)); > > + mutex_unlock(&kvm->lock); > > + if (!rc) > > + return -EINVAL; > > + > > + /* > > + * Mark the userspace range unmerable before adding the pages > > + * in the RMP table. > > + */ > > + mmap_write_lock(kvm->mm); > > + rc = snp_mark_unmergable(kvm, hva, page_level_size(level)); > > + mmap_write_unlock(kvm->mm); > > + if (rc) > > + return -EINVAL; > > + } > > + > > + write_lock(&kvm->mmu_lock); > > + > > + rc = kvm_mmu_get_tdp_walk(vcpu, gpa, &pfn, &npt_level); > > + if (!rc) { > > + /* > > + * This may happen if another vCPU unmapped the page > > + * before we acquire the lock. Retry the PSC. > > + */ > > + write_unlock(&kvm->mmu_lock); > > + return 0; > > + } > > I think we want to return -EAGAIN or similar if we want the caller to > retry, right? I think returning 0 here hides the error. > The problem here is that the caller(linux guest kernel) doesn't retry if PSC fails. The current implementation in the guest kernel is that if a page state change request fails, it terminates the VM with GHCB_TERM_PSC reason. Returning 0 here is not a good option because it will fail the PSC silently and will probably cause a nested RMP fault later. Returning an error also terminates the guest immediately with current guest implementation. I think the best approach here is adding a retry logic to this function. Retrying without returning an error should help it work because snp_check_and_build_npt will be called again and in the second attempt this should work. > > + > > + /* > > + * Adjust the level so that we don't go higher than the backing > > + * page level. > > + */ > > + level = min_t(size_t, level, npt_level); > > + > > + trace_kvm_snp_psc(vcpu->vcpu_id, pfn, gpa, op, level); > > + > > + switch (op) { > > + case SNP_PAGE_STATE_SHARED: > > + rc = snp_make_page_shared(kvm, gpa, pfn, level); > > + break; > > + case SNP_PAGE_STATE_PRIVATE: > > + rc = rmp_make_private(pfn, gpa, level, sev->asid, false); > > + break; > > + default: > > + rc = -EINVAL; > > + break; > > + } > > + > > + write_unlock(&kvm->mmu_lock); > > + > > + if (rc) { > > + pr_err_ratelimited("Error op %d gpa %llx pfn %llx level %d rc %d\n", > > + op, gpa, pfn, level, rc); > > + return rc; > > + } > > + > > + gpa = gpa + page_level_size(level); > > + } > > + > > + return 0; > > +} > > +