On Tue, Apr 04, 2017 at 05:36:33PM +0200, Denys Vlasenko wrote: > > diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S > > index 044d18e..f07b4ef 100644 > > --- a/arch/x86/entry/entry_64.S > > +++ b/arch/x86/entry/entry_64.S > > @@ -265,12 +265,9 @@ return_from_SYSCALL_64: > > * > > * If width of "canonical tail" ever becomes variable, this will need > > * to be updated to remain correct on both old and new CPUs. > > + * > > + * Change top 16 bits to be the sign-extension of 47th bit > > The comment above stops being correct: it's not necessary 16 top bits > we sign-extend now. With larger __VIRTUAL_MASK_SHIFT for 5-level translation, > it will become 7 bits (if I do the math right). Does the patch below look okay to you? > > */ > > - .ifne __VIRTUAL_MASK_SHIFT - 47 > > - .error "virtual address width changed -- SYSRET checks need update" > > - .endif > > - > > - /* Change top 16 bits to be the sign-extension of 47th bit */ > > shl $(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx > > sar $(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx > > The bigger problem here would be the future boot-time choice of 4/5-level > page tables: __VIRTUAL_MASK_SHIFT will need to depend on that choice, > but in this location it is preferable to not use any variables > (memory references). Yeah. Will see what I will be able to come up with. Not sure yet. -------------------8<---------------------- >From 2433cf4f8847bbc41cc2b02d6af4f191b3b5a0c5 Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> Date: Wed, 5 Apr 2017 14:06:15 +0300 Subject: [PATCH] x86/asm: Fix comment in return_from_SYSCALL_64 On x86-64 __VIRTUAL_MASK_SHIFT depends on paging mode now. Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> --- arch/x86/entry/entry_64.S | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 607d72c4a485..c70e064d9592 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -266,7 +266,8 @@ return_from_SYSCALL_64: * If width of "canonical tail" ever becomes variable, this will need * to be updated to remain correct on both old and new CPUs. * - * Change top 16 bits to be the sign-extension of 47th bit + * Change top bits to match most significant valuable bit (47 or 56 + * depending on paging mode) in the address. */ shl $(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx sar $(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx -- Kirill A. Shutemov -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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