On Fri, Jan 05, 2024 at 10:30:23AM -0800, mhkelley58@xxxxxxxxx wrote:
> From: Michael Kelley <mhklinux@xxxxxxxxxxx>
>
> In preparation for temporarily marking pages not present during a
> transition between encrypted and decrypted, use slow_virt_to_phys()
> in the hypervisor callback. As long as the PFN is correct,
> slow_virt_to_phys() works even if the leaf PTE is not present.
> The existing functions that depend on vmalloc_to_page() all
> require that the leaf PTE be marked present, so they don't work.
>
> Update the comments for slow_virt_to_phys() to note this broader usage
> and the requirement to work even if the PTE is not marked present.
>
> Signed-off-by: Michael Kelley <mhklinux@xxxxxxxxxxx>
> ---
> arch/x86/hyperv/ivm.c | 9 ++++++++-
> arch/x86/mm/pat/set_memory.c | 13 +++++++++----
> 2 files changed, 17 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
> index 02e55237d919..8ba18635e338 100644
> --- a/arch/x86/hyperv/ivm.c
> +++ b/arch/x86/hyperv/ivm.c
> @@ -524,7 +524,14 @@ static bool hv_vtom_set_host_visibility(unsigned long kbuffer, int pagecount, bo
> return false;
>
> for (i = 0, pfn = 0; i < pagecount; i++) {
> - pfn_array[pfn] = virt_to_hvpfn((void *)kbuffer + i * HV_HYP_PAGE_SIZE);
> + /*
> + * Use slow_virt_to_phys() because the PRESENT bit has been
> + * temporarily cleared in the PTEs. slow_virt_to_phys() works
> + * without the PRESENT bit while virt_to_hvpfn() or similar
> + * does not.
> + */
> + pfn_array[pfn] = slow_virt_to_phys((void *)kbuffer +
> + i * HV_HYP_PAGE_SIZE) >> HV_HYP_PAGE_SHIFT;
I think you can make it much more readable by introducing few variables:
virt = (void *)kbuffer + i * HV_HYPPAGE_SIZE;
phys = slow_virt_to_phys(virt);
pfn_array[pfn] = phys >> HV_HYP_PAGE_SHIFT;
> pfn++;
>
> if (pfn == HV_MAX_MODIFY_GPA_REP_COUNT || i == pagecount - 1) {
> diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
> index bda9f129835e..8e19796e7ce5 100644
> --- a/arch/x86/mm/pat/set_memory.c
> +++ b/arch/x86/mm/pat/set_memory.c
> @@ -755,10 +755,15 @@ pmd_t *lookup_pmd_address(unsigned long address)
> * areas on 32-bit NUMA systems. The percpu areas can
> * end up in this kind of memory, for instance.
> *
> - * This could be optimized, but it is only intended to be
> - * used at initialization time, and keeping it
> - * unoptimized should increase the testing coverage for
> - * the more obscure platforms.
> + * It is also used in callbacks for CoCo VM page transitions between private
> + * and shared because it works when the PRESENT bit is not set in the leaf
> + * PTE. In such cases, the state of the PTEs, including the PFN, is otherwise
> + * known to be valid, so the returned physical address is correct. The similar
> + * function vmalloc_to_pfn() can't be used because it requires the PRESENT bit.
> + *
> + * This could be optimized, but it is only used in paths that are not perf
> + * sensitive, and keeping it unoptimized should increase the testing coverage
> + * for the more obscure platforms.
> */
> phys_addr_t slow_virt_to_phys(void *__virt_addr)
> {
> --
> 2.25.1
>
--
Kiryl Shutsemau / Kirill A. Shutemov
