forked from SLFO-pool/xen
80 lines
2.6 KiB
Diff
80 lines
2.6 KiB
Diff
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# Commit a2330b51df267e20e66bbba6c5bf08f0570ed58b
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# Date 2024-05-07 16:56:46 +0100
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# Author Andrew Cooper <andrew.cooper3@citrix.com>
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# Committer Andrew Cooper <andrew.cooper3@citrix.com>
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x86/cpu-policy: Fix migration from Ice Lake to Cascade Lake
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Ever since Xen 4.14, there has been a latent bug with migration.
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While some toolstacks can level the features properly, they don't shink
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feat.max_subleaf when all features have been dropped. This is because
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we *still* have not completed the toolstack side work for full CPU Policy
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objects.
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As a consequence, even when properly feature levelled, VMs can't migrate
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"backwards" across hardware which reduces feat.max_subleaf. One such example
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is Ice Lake (max_subleaf=2 for INTEL_PSFD) to Cascade Lake (max_subleaf=0).
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Extend the max policies feat.max_subleaf to the hightest number Xen knows
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about, but leave the default policies matching the host. This will allow VMs
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with a higher feat.max_subleaf than strictly necessary to migrate in.
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Eventually we'll manage to teach the toolstack how to avoid creating such VMs
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in the first place, but there's still more work to do there.
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Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
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Acked-by: Roger Pau Monné <roger.pau@citrix.com>
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--- a/xen/arch/x86/cpu-policy.c
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+++ b/xen/arch/x86/cpu-policy.c
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@@ -603,6 +603,13 @@ static void __init calculate_pv_max_poli
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unsigned int i;
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*p = host_cpu_policy;
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+
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+ /*
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+ * Some VMs may have a larger-than-necessary feat max_subleaf. Allow them
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+ * to migrate in.
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+ */
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+ p->feat.max_subleaf = ARRAY_SIZE(p->feat.raw) - 1;
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+
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x86_cpu_policy_to_featureset(p, fs);
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for ( i = 0; i < ARRAY_SIZE(fs); ++i )
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@@ -643,6 +650,10 @@ static void __init calculate_pv_def_poli
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unsigned int i;
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*p = pv_max_cpu_policy;
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+
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+ /* Default to the same max_subleaf as the host. */
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+ p->feat.max_subleaf = host_cpu_policy.feat.max_subleaf;
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+
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x86_cpu_policy_to_featureset(p, fs);
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for ( i = 0; i < ARRAY_SIZE(fs); ++i )
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@@ -679,6 +690,13 @@ static void __init calculate_hvm_max_pol
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const uint32_t *mask;
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*p = host_cpu_policy;
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+
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+ /*
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+ * Some VMs may have a larger-than-necessary feat max_subleaf. Allow them
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+ * to migrate in.
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+ */
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+ p->feat.max_subleaf = ARRAY_SIZE(p->feat.raw) - 1;
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+
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x86_cpu_policy_to_featureset(p, fs);
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mask = hvm_hap_supported() ?
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@@ -780,6 +798,10 @@ static void __init calculate_hvm_def_pol
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const uint32_t *mask;
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*p = hvm_max_cpu_policy;
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+
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+ /* Default to the same max_subleaf as the host. */
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+ p->feat.max_subleaf = host_cpu_policy.feat.max_subleaf;
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+
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x86_cpu_policy_to_featureset(p, fs);
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mask = hvm_hap_supported() ?
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