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From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: x86/spec-ctrl: Update docs with SRBDS workaround
RDRAND/RDSEED can be hidden using cpuid= to mitigate SRBDS if microcode
isn't available.
This is part of XSA-320 / CVE-2020-0543.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Julien Grall <jgrall@amazon.com>
diff --git a/docs/misc/xen-command-line.pandoc b/docs/misc/xen-command-line.pandoc
index c780312531..81e12d053c 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -481,12 +481,18 @@ choice of `dom0-kernel` is deprecated and not supported by all Dom0 kernels.
This option allows for fine tuning of the facilities Xen will use, after
accounting for hardware capabilities as enumerated via CPUID.
+Unless otherwise noted, options only have any effect in their negative form,
+to hide the named feature(s). Ignoring a feature using this mechanism will
+cause Xen not to use the feature, nor offer them as usable to guests.
+
Currently accepted:
The Speculation Control hardware features `srbds-ctrl`, `md-clear`, `ibrsb`,
`stibp`, `ibpb`, `l1d-flush` and `ssbd` are used by default if available and
-applicable. They can be ignored, e.g. `no-ibrsb`, at which point Xen won't
-use them itself, and won't offer them to guests.
+applicable. They can all be ignored.
+
+`rdrand` and `rdseed` can be ignored, as a mitigation to XSA-320 /
+CVE-2020-0543.
### cpuid_mask_cpu
> `= fam_0f_rev_[cdefg] | fam_10_rev_[bc] | fam_11_rev_b`
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