[Xen-devel] [PATCH v4 09/26] xen/x86: Clear dependent features when clearing a cpu cap

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

When clearing a cpu cap, clear all dependent features.  This avoids having a
featureset with intermediate features disabled, but leaf features enabled.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Jan Beulich <JBeulich@xxxxxxxx>
---
v3:
 * Style fixes.  Use __test_and_set_bit()
---
 xen/arch/x86/cpu/common.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index d302272..0942b44 100644
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -53,8 +53,22 @@ static unsigned int cleared_caps[NCAPINTS];
 
 void __init setup_clear_cpu_cap(unsigned int cap)
 {
+       const uint32_t *dfs;
+       unsigned int i;
+
+       if (__test_and_set_bit(cap, cleared_caps))
+               return;
+
        __clear_bit(cap, boot_cpu_data.x86_capability);
-       __set_bit(cap, cleared_caps);
+       dfs = lookup_deep_deps(cap);
+
+       if (!dfs)
+               return;
+
+       for (i = 0; i < FSCAPINTS; ++i) {
+               cleared_caps[i] |= dfs[i];
+               boot_cpu_data.x86_capability[i] &= ~dfs[i];
+       }
 }
 
 static void default_init(struct cpuinfo_x86 * c)
-- 
2.1.4


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