From patchwork Wed Sep 11 20:41:48 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sean Christopherson X-Patchwork-Id: 13801086 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 1B363EE57D7 for ; Wed, 11 Sep 2024 20:45:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:Reply-To:List-Subscribe:List-Help: List-Post:List-Archive:List-Unsubscribe:List-Id:Cc:To:From:Subject:Message-ID :References:Mime-Version:In-Reply-To:Date:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; 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AJvYcCWn4kT1019/XUPpNZ6cDPWAoZA9cQa07i0HWW3Bsbzae0whS2VQJ6AZpZLMjiEruqfD259QGcCyXvEYHQ==@lists.infradead.org X-Gm-Message-State: AOJu0YxXhIYOPKIcoW6YUdWJKVknHQMN1LVD+Ax0dYtQ0FSRgUAh0ld/ y7kJmlY0OloAZsPr617ef/2IpMSpOm0RQjesh/L0lPxMj1NliB+KMFOQnWEJBB6j7pL3CW+dMS5 ovg== X-Google-Smtp-Source: AGHT+IHjCnU+25WZuBONT4gBCIxwCF19WEi2vWiBq4GXfH9hGN5Xz3FJR6dlFxBZ6NyYinSbokZ9vN2oU0w= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a05:690c:4983:b0:62f:1f63:ae4f with SMTP id 00721157ae682-6dbb6abce79mr220417b3.1.1726087346868; Wed, 11 Sep 2024 13:42:26 -0700 (PDT) Date: Wed, 11 Sep 2024 13:41:48 -0700 In-Reply-To: <20240911204158.2034295-1-seanjc@google.com> Mime-Version: 1.0 References: <20240911204158.2034295-1-seanjc@google.com> X-Mailer: git-send-email 2.46.0.598.g6f2099f65c-goog Message-ID: <20240911204158.2034295-4-seanjc@google.com> Subject: [PATCH v2 03/13] KVM: selftests: Fudge around an apparent gcc bug in arm64's PMU test From: Sean Christopherson To: Marc Zyngier , Oliver Upton , Anup Patel , Paolo Bonzini , Christian Borntraeger , Janosch Frank , Claudio Imbrenda Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, kvm@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, Sean Christopherson , James Houghton X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240911_134229_431848_933EAD73 X-CRM114-Status: GOOD ( 14.82 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Sean Christopherson Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org Use u64_replace_bits() instead of u64p_replace_bits() to set PMCR.N in arm64's vPMU counter access test to fudge around what appears to be a gcc bug. With the recent change to have vcpu_get_reg() return a value in lieu of an out-param, some versions of gcc completely ignore the operation performed by set_pmcr_n(), i.e. ignore the output param. The issue is most easily observed by making set_pmcr_n() noinline and wrapping the call with printf(), e.g. sans comments, for this code: printf("orig = %lx, next = %lx, want = %lu\n", pmcr_orig, pmcr, pmcr_n); set_pmcr_n(&pmcr, pmcr_n); printf("orig = %lx, next = %lx, want = %lu\n", pmcr_orig, pmcr, pmcr_n); gcc-13 generates: 0000000000401c90 : 401c90: f9400002 ldr x2, [x0] 401c94: b3751022 bfi x2, x1, #11, #5 401c98: f9000002 str x2, [x0] 401c9c: d65f03c0 ret 0000000000402660 : 402724: aa1403e3 mov x3, x20 402728: aa1503e2 mov x2, x21 40272c: aa1603e0 mov x0, x22 402730: aa1503e1 mov x1, x21 402734: 940060ff bl 41ab30 <_IO_printf> 402738: aa1403e1 mov x1, x20 40273c: 910183e0 add x0, sp, #0x60 402740: 97fffd54 bl 401c90 402744: aa1403e3 mov x3, x20 402748: aa1503e2 mov x2, x21 40274c: aa1503e1 mov x1, x21 402750: aa1603e0 mov x0, x22 402754: 940060f7 bl 41ab30 <_IO_printf> with the value stored in [sp + 0x60] ignored by both printf() above and in the test proper, resulting in a false failure due to vcpu_set_reg() simply storing the original value, not the intended value. $ ./vpmu_counter_access Random seed: 0x6b8b4567 orig = 3040, next = 3040, want = 0 orig = 3040, next = 3040, want = 0 ==== Test Assertion Failure ==== aarch64/vpmu_counter_access.c:505: pmcr_n == get_pmcr_n(pmcr) pid=71578 tid=71578 errno=9 - Bad file descriptor 1 0x400673: run_access_test at vpmu_counter_access.c:522 2 (inlined by) main at vpmu_counter_access.c:643 3 0x4132d7: __libc_start_call_main at libc-start.o:0 4 0x413653: __libc_start_main at ??:0 5 0x40106f: _start at ??:0 Failed to update PMCR.N to 0 (received: 6) Somewhat bizarrely, gcc-11 also exhibits the same behavior, but only if set_pmcr_n() is marked noinline, whereas gcc-13 fails even if set_pmcr_n() is inlined in its sole caller. All signs point to this being a gcc bug, as clang doesn't exhibit the same issue, the code generated by u64p_replace_bits() is correct, and the error is somewhat transient, e.g. varies between gcc versions and depends on surrounding code. For now, work around the issue to unblock the vcpu_get_reg() cleanup, and because arguably using u64_replace_bits() makes the code a wee bit more intuitive. Signed-off-by: Sean Christopherson --- tools/testing/selftests/kvm/aarch64/vpmu_counter_access.c | 8 +------- 1 file changed, 1 insertion(+), 7 deletions(-) diff --git a/tools/testing/selftests/kvm/aarch64/vpmu_counter_access.c b/tools/testing/selftests/kvm/aarch64/vpmu_counter_access.c index 30d9c9e7ae35..74da8252b884 100644 --- a/tools/testing/selftests/kvm/aarch64/vpmu_counter_access.c +++ b/tools/testing/selftests/kvm/aarch64/vpmu_counter_access.c @@ -45,11 +45,6 @@ static uint64_t get_pmcr_n(uint64_t pmcr) return FIELD_GET(ARMV8_PMU_PMCR_N, pmcr); } -static void set_pmcr_n(uint64_t *pmcr, uint64_t pmcr_n) -{ - u64p_replace_bits((__u64 *) pmcr, pmcr_n, ARMV8_PMU_PMCR_N); -} - static uint64_t get_counters_mask(uint64_t n) { uint64_t mask = BIT(ARMV8_PMU_CYCLE_IDX); @@ -484,13 +479,12 @@ static void test_create_vpmu_vm_with_pmcr_n(uint64_t pmcr_n, bool expect_fail) vcpu = vpmu_vm.vcpu; pmcr_orig = vcpu_get_reg(vcpu, KVM_ARM64_SYS_REG(SYS_PMCR_EL0)); - pmcr = pmcr_orig; /* * Setting a larger value of PMCR.N should not modify the field, and * return a success. */ - set_pmcr_n(&pmcr, pmcr_n); + pmcr = u64_replace_bits(pmcr_orig, pmcr_n, ARMV8_PMU_PMCR_N); vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_PMCR_EL0), pmcr); pmcr = vcpu_get_reg(vcpu, KVM_ARM64_SYS_REG(SYS_PMCR_EL0));