From: Sean Christopherson <seanjc@google.com>
To: Ben Gardon <bgardon@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvm <kvm@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
Brijesh Singh <brijesh.singh@amd.com>,
Tom Lendacky <thomas.lendacky@amd.com>
Subject: Re: [PATCH 03/15] KVM: x86/mmu: Ensure MMU pages are available when allocating roots
Date: Wed, 3 Mar 2021 08:46:59 -0800 [thread overview]
Message-ID: <YD+9gwhfFCS7Xghe@google.com> (raw)
In-Reply-To: <CANgfPd95G-01ObzeKeMTUu0yXBJ=0+ZGQwr_5WCNH-NmR03f9w@mail.gmail.com>
On Tue, Mar 02, 2021, Ben Gardon wrote:
> > @@ -3241,16 +3237,10 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu)
> >
> > if (is_tdp_mmu_enabled(vcpu->kvm)) {
> > root = kvm_tdp_mmu_get_vcpu_root_hpa(vcpu);
> > -
> > - if (!VALID_PAGE(root))
> > - return -ENOSPC;
> > vcpu->arch.mmu->root_hpa = root;
> > } else if (shadow_root_level >= PT64_ROOT_4LEVEL) {
> > root = mmu_alloc_root(vcpu, 0, 0, shadow_root_level,
> > true);
> > -
> > - if (!VALID_PAGE(root))
> > - return -ENOSPC;
>
> There's so much going on in mmu_alloc_root that removing this check
> makes me nervous, but I think it should be safe.
Just think of it as a variant of kvm_mmu_get_page(), then all your fears will
melt away. ;-)
> I checked though the function because I was worried it might yield
> somewhere in there, which could result in the page cache being emptied
> and the allocation failing, but I don't think mmu_alloc_root this
> function will yield.
Ugh, mmu_alloc_root() won't yield, but get_zeroed_page() used to allocate pae_root
and lm_root on-demand in mmu_alloc_shadow_roots() will. The two options are
(a) allocate the fake roots before taking the lock and (b) allocate them from
vcpu->arch.mmu_shadow_page_cache. I probably prefer (a). (b) will slide
directly into the existing code, but would require bumping the min number of
objects for mmu_shadow_page_cache in mmu_topup_memory_caches(). I'd prefer not
to have yet more code that has to deal with this insanity.
next prev parent reply other threads:[~2021-03-04 0:29 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-02 18:45 [PATCH 00/15] KVM: x86/mmu: Lots of bug fixes Sean Christopherson
2021-03-02 18:45 ` [PATCH 01/15] KVM: nSVM: Set the shadow root level to the TDP level for nested NPT Sean Christopherson
2021-03-02 18:45 ` [PATCH 02/15] KVM: x86/mmu: Alloc page for PDPTEs when shadowing 32-bit NPT with 64-bit Sean Christopherson
2021-03-03 17:28 ` Ben Gardon
2021-03-02 18:45 ` [PATCH 03/15] KVM: x86/mmu: Ensure MMU pages are available when allocating roots Sean Christopherson
2021-03-03 0:21 ` Ben Gardon
2021-03-03 16:46 ` Sean Christopherson [this message]
2021-03-02 18:45 ` [PATCH 04/15] KVM: x86/mmu: Allocate the lm_root before allocating PAE roots Sean Christopherson
2021-03-02 18:45 ` [PATCH 05/15] KVM: x86/mmu: Check PDPTRs " Sean Christopherson
2021-03-02 18:45 ` [PATCH 06/15] KVM: x86/mmu: Fix and unconditionally enable WARNs to detect PAE leaks Sean Christopherson
2021-03-02 18:45 ` [PATCH 07/15] KVM: x86/mmu: Use '0' as the one and only value for an invalid PAE root Sean Christopherson
2021-03-02 18:45 ` [PATCH 08/15] KVM: x86/mmu: Set the C-bit in the PDPTRs and LM pseudo-PDPTRs Sean Christopherson
2021-03-02 18:45 ` [PATCH 09/15] KVM: x86/mmu: Mark the PAE roots as decrypted for shadow paging Sean Christopherson
2021-03-02 18:45 ` [PATCH 10/15] KVM: SVM: Don't strip the C-bit from CR2 on #PF interception Sean Christopherson
2021-03-02 18:45 ` [PATCH 11/15] KVM: nVMX: Defer the MMU reload to the normal path on an EPTP switch Sean Christopherson
2021-03-02 18:45 ` [PATCH 12/15] KVM: x86: Defer the MMU unload to the normal path on an global INVPCID Sean Christopherson
2021-03-02 18:45 ` [PATCH 13/15] KVM: x86/mmu: Unexport MMU load/unload functions Sean Christopherson
2021-03-02 18:45 ` [PATCH 14/15] KVM: x86/mmu: Sync roots after MMU load iff load as successful Sean Christopherson
2021-03-02 18:45 ` [PATCH 15/15] KVM: x86/mmu: WARN on NULL pae_root and bad shadow root level Sean Christopherson
Reply instructions:
You may reply publicly 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=YD+9gwhfFCS7Xghe@google.com \
--to=seanjc@google.com \
--cc=bgardon@google.com \
--cc=brijesh.singh@amd.com \
--cc=jmattson@google.com \
--cc=joro@8bytes.org \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=pbonzini@redhat.com \
--cc=thomas.lendacky@amd.com \
--cc=vkuznets@redhat.com \
--cc=wanpengli@tencent.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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.