From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-yw1-f202.google.com (mail-yw1-f202.google.com [209.85.128.202]) (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 B98241798E for ; Wed, 13 Sep 2023 17:46:13 +0000 (UTC) Received: by mail-yw1-f202.google.com with SMTP id 00721157ae682-58c9d29588aso1173917b3.0 for ; Wed, 13 Sep 2023 10:46:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1694627172; x=1695231972; darn=lists.linux.dev; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=/ocbK288Al1DpwUeolIoLVHrflqgxdyru7h8mWey0wo=; b=qBQ9qFw2WCzIZkH5hYYTtov+D+32jK8mDWgpdKD/YvAGGkk/kh7Z0njbgiw8eYIes0 JIgOop1YtUPXIkL3/2/5ShWVbmF9h1zD+nUnTqw98rC5AJVRT6Wwf7LN1i5JphBLaW1e sdQqyxxfe58XvxTccQs2Vyxi/qr4np4CVAceqtYZSbKD7+olgktF20sZo28t26g+WbiS YyrrMcR1jJE5v9F+P4D2oSZL6IDK9XOCPMK/gxUNJni54QqScHKxSVEQSjYFqey/rcMg XNg1UonSaQdrDMeEB8khSVpM8csJxO1Fc+xyMqLpDkBqtkwDhwgs6dS+DJPEAT/kXJTW g8FA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1694627172; x=1695231972; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=/ocbK288Al1DpwUeolIoLVHrflqgxdyru7h8mWey0wo=; b=K5OSzNkjKicUEE7rj3U+U60FEBsAcXW/cZzWsa4qlI2WRYpjohUhQOLll+jzv/HM4w ES+0NEQEhF96kLKgmDGLMYYhdEMDT30iV7z8nZyGekOrDAjHctG4sX2stQwN5gO+oHtB 8jTh5DXY+1R2CP/eSRveduk5qVRxcApEqpYc/v0yTKbjCbtalf3IpD7k8d7+pE3R+/cW OsJHBZibtBMWqK7NKXBGnzWaNl8xQYzfDStxx89liQqjDq1w+t5OKc91VmIsQwyv4JlC hxMFOXakBn/0Q/nyiVHp44+ddcYWmxSL8e5Sajv+0LPHTKlk4IUR1q3U7gVhyRkybiEk yxUw== X-Gm-Message-State: AOJu0YyJ5AKYFy80nIsa/v/0Sh6eHoijxvhuoEzDX2yGA2amBOV/wHyj LNhQHlbLuAbRJFYLrL+kKiDfkLLGFzo= X-Google-Smtp-Source: AGHT+IEL/dshnjsgmjdfGSman4r0qxwjXyMs+hXHniVftyWUrPYv6azBgo0B81bsYJN3JcUy4Fmp/3PNp8E= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a05:6902:1102:b0:d0b:d8cd:e661 with SMTP id o2-20020a056902110200b00d0bd8cde661mr95997ybu.12.1694627172692; Wed, 13 Sep 2023 10:46:12 -0700 (PDT) Date: Wed, 13 Sep 2023 10:46:11 -0700 In-Reply-To: <852b6fa117bf3767a99353d908bc566a5dd9c61a.1694599703.git.isaku.yamahata@intel.com> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <852b6fa117bf3767a99353d908bc566a5dd9c61a.1694599703.git.isaku.yamahata@intel.com> Message-ID: Subject: Re: [RFC PATCH 4/6] KVM: guest_memfd: Implemnet bmap inode operation From: Sean Christopherson To: isaku.yamahata@intel.com Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, isaku.yamahata@gmail.com, Michael Roth , Paolo Bonzini , erdemaktas@google.com, Sagi Shahar , David Matlack , Kai Huang , Zhi Wang , chen.bo@intel.com, linux-coco@lists.linux.dev, Chao Peng , Ackerley Tng , Vishal Annapurve , Yuan Yao , Jarkko Sakkinen , Xu Yilun , Quentin Perret , wei.w.wang@intel.com, Fuad Tabba Content-Type: text/plain; charset="us-ascii" On Wed, Sep 13, 2023, isaku.yamahata@intel.com wrote: > From: Isaku Yamahata > > To inject memory failure, physical address of the page is needed. > Implement bmap() method to convert the file offset into physical address. > > Signed-off-by: Isaku Yamahata > --- > virt/kvm/Kconfig | 4 ++++ > virt/kvm/guest_mem.c | 28 ++++++++++++++++++++++++++++ > 2 files changed, 32 insertions(+) > > diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig > index 624df45baff0..eb008f0e7cc3 100644 > --- a/virt/kvm/Kconfig > +++ b/virt/kvm/Kconfig > @@ -115,3 +115,7 @@ config KVM_GENERIC_PRIVATE_MEM > > config HAVE_GENERIC_PRIVATE_MEM_HANDLE_ERROR > bool > + > +config KVM_GENERIC_PRIVATE_MEM_BMAP > + depends on KVM_GENERIC_PRIVATE_MEM > + bool > diff --git a/virt/kvm/guest_mem.c b/virt/kvm/guest_mem.c > index 3678287d7c9d..90dfdfab1f8c 100644 > --- a/virt/kvm/guest_mem.c > +++ b/virt/kvm/guest_mem.c > @@ -355,12 +355,40 @@ static int kvm_gmem_error_page(struct address_space *mapping, struct page *page) > return MF_DELAYED; > } > > +#ifdef CONFIG_KVM_GENERIC_PRIVATE_MEM_BMAP > +static sector_t kvm_gmem_bmap(struct address_space *mapping, sector_t block) > +{ > + struct folio *folio; > + sector_t pfn = 0; > + > + filemap_invalidate_lock_shared(mapping); > + > + if (block << PAGE_SHIFT > i_size_read(mapping->host)) > + goto out; > + > + folio = filemap_get_folio(mapping, block); > + if (IS_ERR_OR_NULL(folio)) > + goto out; > + > + pfn = folio_pfn(folio) + (block - folio->index); > + folio_put(folio); > + > +out: > + filemap_invalidate_unlock_shared(mapping); > + return pfn; IIUC, hijacking bmap() is a gigantic hack to propagate a host pfn to userspace without adding a new ioctl() or syscall. If we want to support target injection, I would much, much rather add a KVM ioctl(), e.g. to let userspace inject errors for a gfn. Returning a pfn for something that AFAICT has nothing to do with pfns is gross, e.g. the whole "0 is the error code" thing is technically wrong because '0' is a perfectly valid pfn. My vote is to drop this and not extend the injection information for the initial merge, i.e. rely on point testing to verify kvm_gmem_error_page(), and defer adding uAPI to let selftests inject errors. > + > +} > +#endif > + > static const struct address_space_operations kvm_gmem_aops = { > .dirty_folio = noop_dirty_folio, > #ifdef CONFIG_MIGRATION > .migrate_folio = kvm_gmem_migrate_folio, > #endif > .error_remove_page = kvm_gmem_error_page, > +#ifdef CONFIG_KVM_GENERIC_PRIVATE_MEM_BMAP > + .bmap = kvm_gmem_bmap, > +#endif > }; > > static int kvm_gmem_getattr(struct mnt_idmap *idmap, > -- > 2.25.1 >