x86/kvm/mmu: reset MMU context when 32-bit guest switches PAE [Linux 5.1]

x86/kvm/mmu: reset MMU context when 32-bit guest switches PAE [Linux 5.1]

This Linux kernel change "x86/kvm/mmu: reset MMU context when 32-bit guest switches PAE" is included in the Linux 5.1 release. This change is authored by Vitaly Kuznetsov <vkuznets [at] redhat.com> on Tue Apr 30 19:33:26 2019 +0200. The commit for this change in Linux stable tree is 0699c64 (patch).

x86/kvm/mmu: reset MMU context when 32-bit guest switches PAE

Commit 47c42e6b4192 ("KVM: x86: fix handling of role.cr4_pae and rename it
to 'gpte_size'") introduced a regression: 32-bit PAE guests stopped
working. The issue appears to be: when guest switches (enables) PAE we need
to re-initialize MMU context (set context->root_level, do
reset_rsvds_bits_mask(), ...) but init_kvm_tdp_mmu() doesn't do that
because we threw away is_pae(vcpu) flag from mmu role. Restore it to
kvm_mmu_extended_role (as we now don't need it in base role) to fix
the issue.

Fixes: 47c42e6b4192 ("KVM: x86: fix handling of role.cr4_pae and rename it to 'gpte_size'")
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

There are 2 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 arch/x86/include/asm/kvm_host.h | 1 +
 arch/x86/kvm/mmu.c              | 1 +
 2 files changed, 2 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index a9d03af..c79abe7 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -295,6 +295,7 @@ struct kvm_mmu_memory_cache {
        unsigned int valid:1;
        unsigned int execonly:1;
        unsigned int cr0_pg:1;
+       unsigned int cr4_pae:1;
        unsigned int cr4_pse:1;
        unsigned int cr4_pke:1;
        unsigned int cr4_smap:1;
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index e10962d..d9c7b45 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -4781,6 +4781,7 @@ static union kvm_mmu_extended_role kvm_calc_mmu_role_ext(struct kvm_vcpu *vcpu)
    union kvm_mmu_extended_role ext = {0};

    ext.cr0_pg = !!is_paging(vcpu);
+   ext.cr4_pae = !!is_pae(vcpu);
    ext.cr4_smep = !!kvm_read_cr4_bits(vcpu, X86_CR4_SMEP);
    ext.cr4_smap = !!kvm_read_cr4_bits(vcpu, X86_CR4_SMAP);
    ext.cr4_pse = !!is_pse(vcpu);

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