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Peter Anvin" Subject: [PATCH] x86/pat: fix pat_x_mtrr_type() for MTRR disabled case Date: Tue, 10 Jan 2023 07:54:27 +0100 Message-Id: <20230110065427.20767-1-jgross@suse.com> X-Mailer: git-send-email 2.35.3 MIME-Version: 1.0 X-Spam-Status: No, score=-4.4 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED,SPF_HELO_NONE, SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1754617682676232543?= X-GMAIL-MSGID: =?utf-8?q?1754617682676232543?= Since commit 72cbc8f04fe2 ("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(). Fixes: 72cbc8f04fe2 ("x86/PAT: Have pat_enabled() properly reflect state when running on Xen") Reported-by: Michael Kelley (LINUX) Signed-off-by: Juergen Gross Reviewed-by: Michael Kelley Tested-by: Michael Kelley --- arch/x86/mm/pat/memtype.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/mm/pat/memtype.c b/arch/x86/mm/pat/memtype.c index 46de9cf5c91d..fb4b1b5e0dea 100644 --- a/arch/x86/mm/pat/memtype.c +++ b/arch/x86/mm/pat/memtype.c @@ -387,7 +387,8 @@ static unsigned long pat_x_mtrr_type(u64 start, u64 end, u8 mtrr_type, uniform; mtrr_type = mtrr_type_lookup(start, end, &uniform); - if (mtrr_type != MTRR_TYPE_WRBACK) + if (mtrr_type != MTRR_TYPE_WRBACK && + mtrr_type != MTRR_TYPE_INVALID) return _PAGE_CACHE_MODE_UC_MINUS; return _PAGE_CACHE_MODE_WB;