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Peter Anvin" , Peter Zijlstra , Pawan Gupta , Josh Poimboeuf , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/2] x86/cpu: Refactor RFDS mitigation to use X86_FEATURE_RFDS_CLEAR Message-ID: <20260130214026.GEaX0lSoVqbM9lInfr@fat_crate.local> References: <20260129154342.3867-1-moontorise@cfg.kr> <20260130123340.1544-1-moontorise@cfg.kr> <20260130123340.1544-2-moontorise@cfg.kr> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260130123340.1544-2-moontorise@cfg.kr> On Fri, Jan 30, 2026 at 09:33:39PM +0900, Joongsun Moon-Lee wrote: > The current RFDS mitigation logic relies on verw_clears_cpu_reg_file(), > which directly checks the RFDS_CLEAR bit in the IA32_ARCH_CAPABILITIES MSR. > > To support quirks for CPUs that mitigate RFDS but do not enumerate it, > transition to using the synthetic feature flag X86_FEATURE_RFDS_CLEAR. > > Replace the MSR-bit-based check with boot_cpu_has(X86_FEATURE_RFDS_CLEAR) > and synthesize this feature bit in rfds_select_mitigation() if the > architectural RFDS_CLEAR bit is present. Please do not explain the diff - talk about why this patch exists and other details which are not obvious from the code. > @@ -670,7 +665,10 @@ static void __init rfds_select_mitigation(void) > if (rfds_mitigation == RFDS_MITIGATION_OFF) > return; > > - if (verw_clears_cpu_reg_file()) > + if (x86_arch_cap_msr & ARCH_CAP_RFDS_CLEAR) > + setup_force_cpu_cap(X86_FEATURE_RFDS_CLEAR); > + > + if (boot_cpu_has(X86_FEATURE_RFDS_CLEAR)) > verw_clear_cpu_buf_mitigation_selected = true; > } So: if (x86_arch_cap_msr & ARCH_CAP_RFDS_CLEAR) { setup_force_cpu_cap(X86_FEATURE_RFDS_CLEAR); verw_clear_cpu_buf_mitigation_selected = true; } ? -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette