Re: [PATCH 1/1] target/i386/mshv: fix read/write memory across the page boundary

[Magnus Kulke <magnuskulke@linux.microsoft.com>]

On Thu, Apr 09, 2026 at 08:53:34PM +0300, Doru Blânzeanu wrote:
> Previously, read_memory and write_memory performed a single GVA-to-GPA
> translation for the entire buffer. If the buffer spanned a page
> boundary, the translated GPA was only valid for the first page, causing
> incorrect reads/writes for the remainder.
> 
> Fix both functions to loop over pages, translating and accessing each
> page-aligned chunk separately.
> 
> Signed-off-by: Doru Blânzeanu <dblanzeanu@linux.microsoft.com>
> ---
>  target/i386/mshv/mshv-cpu.c | 71 +++++++++++++++++++++++++++----------
>  1 file changed, 52 insertions(+), 19 deletions(-)
> 
> diff --git a/target/i386/mshv/mshv-cpu.c b/target/i386/mshv/mshv-cpu.c
> index 2bc978deb2..afdb6b6e29 100644
> --- a/target/i386/mshv/mshv-cpu.c
> +++ b/target/i386/mshv/mshv-cpu.c
> @@ -1316,21 +1316,38 @@ static int read_memory(const CPUState *cpu, uint64_t initial_gva,
>  {
>      int ret;
>      uint64_t gpa, flags;
> -
> -    if (gva == initial_gva) {
> -        gpa = initial_gpa;
> -    } else {
> -        flags = HV_TRANSLATE_GVA_VALIDATE_READ;
> -        ret = translate_gva(cpu, gva, &gpa, flags);
> -        if (ret < 0) {
> -            return -1;
> +    uint64_t cur_gva = gva;
> +    size_t page_left, chunk;
> +    uint8_t *cur_data = data;
> +
> +    /*
> +     * If the read spans multiple pages,
> +     * we need to translate and read each page separately
> +     */
> +    while (len > 0) {
> +        page_left = HV_HYP_PAGE_SIZE - (cur_gva & (HV_HYP_PAGE_SIZE - 1));
> +        chunk = MIN(len, page_left);
> +
> +        if (cur_gva == initial_gva) {
> +            gpa = initial_gpa;
> +        } else {
> +            flags = HV_TRANSLATE_GVA_VALIDATE_READ;
> +            ret = translate_gva(cpu, cur_gva, &gpa, flags);
> +            if (ret < 0) {
> +                return -1;
> +            }
>          }
>  
> -        ret = mshv_guest_mem_read(gpa, data, len, false, false);
> +        ret = mshv_guest_mem_read(gpa, cur_data, chunk,
> +                                  false, false);
>          if (ret < 0) {
>              error_report("failed to read guest mem");
>              return -1;
>          }
> +
> +        cur_gva += chunk;
> +        cur_data += chunk;
> +        len -= chunk;
>      }
>  
>      return 0;
> @@ -1341,18 +1358,34 @@ static int write_memory(const CPUState *cpu, uint64_t gva, const uint8_t *data,
>  {
>      int ret;
>      uint64_t gpa, flags;
> +    uint64_t cur_gva = gva;
> +    size_t page_left, chunk;
> +    const uint8_t *cur_data = data;
> +
> +    /*
> +     * If the write spans multiple pages,
> +     * we need to translate and write each page separately
> +     */
> +    while (len > 0) {
> +        page_left = HV_HYP_PAGE_SIZE - (cur_gva & (HV_HYP_PAGE_SIZE - 1));
> +        chunk = MIN(len, page_left);
> +
> +        flags = HV_TRANSLATE_GVA_VALIDATE_WRITE;
> +        ret = translate_gva(cpu, cur_gva, &gpa, flags);
> +        if (ret < 0) {
> +            error_report("failed to translate gva to gpa");
> +            return -1;
> +        }
>  
> -    flags = HV_TRANSLATE_GVA_VALIDATE_WRITE;
> -    ret = translate_gva(cpu, gva, &gpa, flags);
> -    if (ret < 0) {
> -        error_report("failed to translate gva to gpa");
> -        return -1;
> -    }
> +        ret = mshv_guest_mem_write(gpa, cur_data, chunk, false);
> +        if (ret != MEMTX_OK) {
> +            error_report("failed to write to mmio");
> +            return -1;
> +        }
>  
> -    ret = mshv_guest_mem_write(gpa, data, len, false);
> -    if (ret != MEMTX_OK) {
> -        error_report("failed to write to mmio");
> -        return -1;
> +        cur_gva += chunk;
> +        cur_data += chunk;
> +        len -= chunk;
>      }
>  
>      return 0;
> -- 
> 2.53.0

Fixes: 6dec60528c (target/i386/mshv: Implement mshv_vcpu_run())