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    SubjectRe: [PATCH v7 14/22] x86/decompressor: Merge trampoline cleanup with switching code
    On Tue, 1 Aug 2023 at 14:09, Borislav Petkov <bp@alien8.de> wrote:
    >
    > On Fri, Jul 28, 2023 at 11:09:08AM +0200, Ard Biesheuvel wrote:
    > > diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
    > > index 4016444e6788304f..4f50af23a0854f18 100644
    > > --- a/arch/x86/boot/compressed/pgtable_64.c
    > > +++ b/arch/x86/boot/compressed/pgtable_64.c
    > > @@ -101,9 +101,10 @@ static unsigned long find_trampoline_placement(void)
    > > return bios_start - TRAMPOLINE_32BIT_SIZE;
    > > }
    > >
    > > -asmlinkage void set_paging_levels(void *rmode)
    > > +asmlinkage void set_paging_levels(void *rmode, void *pgtable)
    >
    > Please get rid of this silly rmode arg which gets passed in here as
    > boot_params and then gets assigned to an extern pointer to boot_params.
    > This is just silly. Just do what the other functions get from %r15 now
    > - a struct boot_params *bp arg.
    >
    > But perhaps in a separate patch.
    >

    OK

    > > {
    > > void (*toggle_la57)(void *trampoline, bool enable_5lvl);
    > > + void *trampoline_pgtable;
    > > bool l5_required = false;
    > >
    > > /* Initialize boot_params. Required for cmdline_find_option_bool(). */
    > > @@ -133,7 +134,7 @@ asmlinkage void set_paging_levels(void *rmode)
    > > * the desired one.
    > > */
    > > if (l5_required == !!(native_read_cr4() & X86_CR4_LA57))
    > > - return;
    > > + goto out;
    > >
    > > trampoline_32bit = (unsigned long *)find_trampoline_placement();
    > >
    > > @@ -163,6 +164,8 @@ asmlinkage void set_paging_levels(void *rmode)
    > > * The new page table will be used by trampoline code for switching
    > > * from 4- to 5-level paging or vice versa.
    > > */
    > > + trampoline_pgtable = trampoline_32bit +
    > > + TRAMPOLINE_32BIT_PGTABLE_OFFSET / sizeof(unsigned long);
    > >
    > > if (l5_required) {
    > > /*
    > > @@ -182,31 +185,21 @@ asmlinkage void set_paging_levels(void *rmode)
    > > * may be above 4G.
    > > */
    > > src = *(unsigned long *)__native_read_cr3() & PAGE_MASK;
    > > - memcpy(trampoline_32bit + TRAMPOLINE_32BIT_PGTABLE_OFFSET / sizeof(unsigned long),
    > > - (void *)src, PAGE_SIZE);
    > > + memcpy(trampoline_pgtable, (void *)src, PAGE_SIZE);
    > > }
    > >
    > > toggle_la57(trampoline_32bit, l5_required);
    > > -}
    > > -
    > > -void cleanup_trampoline(void *pgtable)
    > > -{
    > > - void *trampoline_pgtable;
    > > -
    > > - trampoline_pgtable = trampoline_32bit + TRAMPOLINE_32BIT_PGTABLE_OFFSET / sizeof(unsigned long);
    > >
    > > /*
    > > - * Move the top level page table out of trampoline memory,
    > > - * if it's there.
    > > + * Move the top level page table out of trampoline memory.
    > > */
    > > - if ((void *)__native_read_cr3() == trampoline_pgtable) {
    > > - memcpy(pgtable, trampoline_pgtable, PAGE_SIZE);
    > > - native_write_cr3((unsigned long)pgtable);
    > > - }
    > > + memcpy(pgtable, trampoline_pgtable, PAGE_SIZE);
    > > + native_write_cr3((unsigned long)pgtable);
    > >
    > > /* Restore trampoline memory */
    > > memcpy(trampoline_32bit, trampoline_save, TRAMPOLINE_32BIT_SIZE);
    > >
    > > +out:
    > > /* Initialize variables for 5-level paging */
    > > #ifdef CONFIG_X86_5LEVEL
    > > if (__read_cr4() & X86_CR4_LA57) {
    > > @@ -215,4 +208,5 @@ void cleanup_trampoline(void *pgtable)
    > > ptrs_per_p4d = 512;
    > > }
    > > #endif
    > > + return;
    >
    > No need for that one. It'll return without it. :-)
    >

    Removing it breaks the build for !CONFIG_X86_5LEVEL

    However, I can move these assignments into the conditional at the top
    of the function (the one that sets l5_required) so we don't need the
    label at all. Will fix for v8

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