KVM Archive on lore.kernel.org
 help / color / Atom feed
From: Sean Christopherson <sean.j.christopherson@intel.com>
To: "Paolo Bonzini" <pbonzini@redhat.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>
Cc: kvm@vger.kernel.org, Jiri Palecek <jpalecek@web.de>
Subject: [PATCH] KVM: x86/mmu: Allocate PAE root array when using SVM's 32-bit NPT
Date: Thu, 13 Jun 2019 10:22:23 -0700
Message-ID: <20190613172223.17119-1-sean.j.christopherson@intel.com> (raw)

SVM's Nested Page Tables (NPT) reuses x86 paging for the host-controlled
page walk.  For 32-bit KVM, this means PAE paging is used even when TDP
is enabled, i.e. the PAE root array needs to be allocated.

Fixes: ee6268ba3a68 ("KVM: x86: Skip pae_root shadow allocation if tdp enabled")
Cc: stable@vger.kernel.org
Reported-by: Jiri Palecek <jpalecek@web.de>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---

Jiri, can you please test this patch?  I haven't actually verified this
fixes the bug due to lack of SVM hardware.

 arch/x86/kvm/mmu.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 1e9ba81accba..d3c3d5e5ffd4 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -5602,14 +5602,18 @@ static int alloc_mmu_pages(struct kvm_vcpu *vcpu)
 	struct page *page;
 	int i;
 
-	if (tdp_enabled)
-		return 0;
-
 	/*
-	 * When emulating 32-bit mode, cr3 is only 32 bits even on x86_64.
-	 * Therefore we need to allocate shadow page tables in the first
-	 * 4GB of memory, which happens to fit the DMA32 zone.
+	 * When using PAE paging, the four PDPTEs are treated as 'root' pages,
+	 * while the PDP table is a per-vCPU construct that's allocated at MMU
+	 * creation.  When emulating 32-bit mode, cr3 is only 32 bits even on
+	 * x86_64.  Therefore we need to allocate the PDP table in the first
+	 * 4GB of memory, which happens to fit the DMA32 zone.  Except for
+	 * SVM's 32-bit NPT support, TDP paging doesn't use PAE paging and can
+	 * skip allocating the PDP table.
 	 */
+	if (tdp_enabled && kvm_x86_ops->get_tdp_level(vcpu) > PT32E_ROOT_LEVEL)
+		return 0;
+
 	page = alloc_page(GFP_KERNEL_ACCOUNT | __GFP_DMA32);
 	if (!page)
 		return -ENOMEM;
-- 
2.21.0


             reply index

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-13 17:22 Sean Christopherson [this message]
2019-06-17 13:07 ` Jiri Palecek
2019-06-18 17:04 ` Paolo Bonzini

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20190613172223.17119-1-sean.j.christopherson@intel.com \
    --to=sean.j.christopherson@intel.com \
    --cc=jpalecek@web.de \
    --cc=kvm@vger.kernel.org \
    --cc=pbonzini@redhat.com \
    --cc=rkrcmar@redhat.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

KVM Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/kvm/0 kvm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 kvm kvm/ https://lore.kernel.org/kvm \
		kvm@vger.kernel.org
	public-inbox-index kvm

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.kvm


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git