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Juergen Gross authored
Since 72cbc8f0 ("x86/PAT: Have pat_enabled() properly reflect state when running on Xen") PAT can be enabled without MTRR. This has resulted in problems e.g. for a SEV-SNP guest running under Hyper-V, when trying to establish a new mapping via memremap() with WB caching mode, as pat_x_mtrr_type() will call mtrr_type_lookup(), which in turn is returning MTRR_TYPE_INVALID due to MTRR being disabled in this configuration. The result is a mapping with UC- caching, leading to severe performance degradation. Fix that by handling MTRR_TYPE_INVALID the same way as MTRR_TYPE_WRBACK in pat_x_mtrr_type() because MTRR_TYPE_INVALID means MTRRs are disabled. [ bp: Massage commit message. ] Fixes: 72cbc8f0 ("x86/PAT: Have pat_enabled() properly reflect state when running on Xen") Reported-by:
Michael Kelley (LINUX) <mikelley@microsoft.com> Signed-off-by:
Juergen Gross <jgross@suse.com> Signed-off-by:
Borislav Petkov (AMD) <bp@alien8.de> Reviewed-by:
Michael Kelley <mikelley@microsoft.com> Tested-by:
Michael Kelley <mikelley@microsoft.com> Cc: <stable@kernel.org> Link: https://lore.kernel.org/r/20230110065427.20767-1-jgross@suse.com
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