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[207.172.141.204]) by smtp.gmail.com with ESMTPSA id c21-20020a05620a201500b007831ffa4234sm5285373qka.42.2024.01.25.10.28.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 25 Jan 2024 10:28:39 -0800 (PST) From: Jason Andryuk To: linux-kernel@vger.kernel.org Cc: Jason Andryuk , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" Subject: [PATCH] x86/mm/cpa-test: Ensure pfn isn't already in use Date: Thu, 25 Jan 2024 13:28:35 -0500 Message-ID: <20240125182837.52467-1-jandryuk@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Ensure pfn isn't already in use before assigning to addr[i]. Retry if in use. The subsequent pfns were checked against the bitmap, but not the initial selection. This prevents some false positives on a machine with a small amount of RAM where pfn collisions are more likely to be seen. A Xen HVM first showed: [ 3640.227939] CPA ffff88800869c000: bad pte 800000000869c163 [ 3640.227982] CPA ffff88800104e000: bad pte 800000000104e161 Testing this patch with a Xen PV guest with one 192MB of RAM showed varying numbers of addresses like: [ 2768.082971] CPA test 5 pfn 930d in use Signed-off-by: Jason Andryuk --- This could infinite loop on a machine with a small amount of RAM - is that worth handling? Just skip an in-use pfn instead? --- arch/x86/mm/pat/cpa-test.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/arch/x86/mm/pat/cpa-test.c b/arch/x86/mm/pat/cpa-test.c index ad3c1feec990..bbf337e3e246 100644 --- a/arch/x86/mm/pat/cpa-test.c +++ b/arch/x86/mm/pat/cpa-test.c @@ -136,7 +136,14 @@ static int pageattr_test(void) failed +=3D print_split(&sa); =20 for (i =3D 0; i < NTEST; i++) { - unsigned long pfn =3D get_random_u32_below(max_pfn_mapped); + unsigned long pfn; + + retry: + pfn =3D get_random_u32_below(max_pfn_mapped); + if (test_bit(pfn, bm)) { + pr_debug("CPA test %d pfn %lx in use\n", i, pfn); + goto retry; + } =20 addr[i] =3D (unsigned long)__va(pfn << PAGE_SHIFT); len[i] =3D get_random_u32_below(NPAGES); --=20 2.43.0