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i386: Mask SVM features if nested SVM is disabled 

QEMU incorrectly validates FEAT_SVM feature flags against
GET_SUPPORTED_CPUID even if SVM features are being masked out by
cpu_x86_cpuid().  This can make QEMU print warnings on most AMD
CPU models, even when SVM nesting is disabled (which is the
default).

This bug was never detected before because of a Linux KVM bug:
until Linux v5.6, KVM was not filtering out SVM features in
GET_SUPPORTED_CPUID when nested was disabled.  This KVM bug was
fixed in Linux v5.7-rc1, on Linux commit a50718cc3f43 ("KVM:
nSVM: Expose SVM features to L1 iff nested is enabled").

Fix the problem by adding a CPUID_EXT3_SVM dependency to all
FEAT_SVM feature flags in the feature_dependencies table.

Reported-by: Yanan Fu <yfu@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20200623230116.277409-1-ehabkost@redhat.com>
[Fix testcase. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Eduardo Habkost 2020-06-23 19:01:16 -04:00 committed by Paolo Bonzini
parent c8d7fd059d
commit 730319aef0
2 changed files with 6 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
target/i386/cpu.c
View File

@ -1404,6 +1404,10 @@ static FeatureDep feature_dependencies[] = {
.from = { FEAT_VMX_SECONDARY_CTLS, VMX_SECONDARY_EXEC_ENABLE_VMFUNC },
.to = { FEAT_VMX_VMFUNC, ~0ull },
},
{
.from = { FEAT_8000_0001_ECX, CPUID_EXT3_SVM },
.to = { FEAT_SVM, ~0ull },
},
};
typedef struct X86RegisterInfo32 {

4
tests/qtest/test-x86-cpuid-compat.c
View File

@ -256,7 +256,7 @@ int main(int argc, char **argv)
"-cpu 486,+invtsc", "xlevel", 0x80000007);
/* CPUID[8000_000A].EDX: */
add_cpuid_test("x86/cpuid/auto-xlevel/486/npt",
"-cpu 486,+npt", "xlevel", 0x8000000A);
"-cpu 486,+svm,+npt", "xlevel", 0x8000000A);
/* CPUID[C000_0001].EDX: */
add_cpuid_test("x86/cpuid/auto-xlevel2/phenom/xstore",
"-cpu phenom,+xstore", "xlevel2", 0xC0000001);
@ -348,7 +348,7 @@ int main(int argc, char **argv)
"-machine pc-i440fx-2.4 -cpu SandyBridge,",
"xlevel", 0x80000008);
add_cpuid_test("x86/cpuid/xlevel-compat/pc-i440fx-2.4/npt-on",
"-machine pc-i440fx-2.4 -cpu SandyBridge,+npt",
"-machine pc-i440fx-2.4 -cpu SandyBridge,+svm,+npt",
"xlevel", 0x80000008);
/* Test feature parsing */