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Date: Tue, 28 Sep 2021 16:10:39 -0700 From: "Luck, Tony" <tony.luck@...el.com> To: Dave Hansen <dave.hansen@...el.com> Cc: Andy Lutomirski <luto@...nel.org>, Fenghua Yu <fenghua.yu@...el.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, "Peter Zijlstra (Intel)" <peterz@...radead.org>, Lu Baolu <baolu.lu@...ux.intel.com>, Joerg Roedel <joro@...tes.org>, Josh Poimboeuf <jpoimboe@...hat.com>, Dave Jiang <dave.jiang@...el.com>, Jacob Jun Pan <jacob.jun.pan@...el.com>, Raj Ashok <ashok.raj@...el.com>, "Shankar, Ravi V" <ravi.v.shankar@...el.com>, iommu@...ts.linux-foundation.org, the arch/x86 maintainers <x86@...nel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 4/8] x86/traps: Demand-populate PASID MSR via #GP Moving beyond pseudo-code and into compiles-but-probably-broken-code. The intent of the functions below is that Fenghua should be able to do: void fpu__pasid_write(u32 pasid) { u64 msr_val = pasid | MSR_IA32_PASID_VALID; struct ia32_pasid_state *addr; addr = begin_update_one_xsave_feature(current, XFEATURE_PASID, true); addr->pasid = msr_val; finish_update_one_xsave_feature(current); } So here's the two new functions that would be added to arch/x86/kernel/fpu/xstate.c ---- void *begin_update_one_xsave_feature(struct task_struct *tsk, enum xfeature xfeature, bool full) { struct xregs_state *xsave = &tsk->thread.fpu.state.xsave; struct xregs_state *xinit = &init_fpstate.xsave; u64 fmask = 1ull << xfeature; void *addr; BUG_ON(!(xsave->header.xcomp_bv & fmask)); fpregs_lock(); addr = __raw_xsave_addr(xsave, xfeature); if (full || tsk != current) { memcpy(addr, __raw_xsave_addr(xinit, xfeature), xstate_sizes[xfeature]); goto out; } /* could optimize some cases where xsaves() isn't fastest option */ if (!(xsave->header.xfeatures & fmask)) xsaves(xsave, fmask); out: xsave->header.xfeatures |= fmask; return addr; } void finish_update_one_xsave_feature(struct task_struct *tsk) { set_ti_thread_flag(task_thread_info(tsk), TIF_NEED_FPU_LOAD); fpregs_unlock(); } ---- -Tony
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